Do One's Duty To/With/By Smb?

Avangi

• I have always done my duty ___ my students.

I have always done interesting things with my students.
I have always done well by my students. --> What does this sentence mean?
I have always done my duty to my students.
I'm thinking of the Boy Scout Oath I learned as a child: "On my honor I will do my best to do my duty to God and my country, etc."

--> So you would prefer "to", right?

• The boy was called ___ by his grandfather.

I don't think so. Children are usually named by their parents, and the verb is "to name." The grandfather would more likely make up a nickname for the boy. The boy was called "Sonny" by his grandfather. Are there no optional choices offered? The preposition "by" is already there! What kind of word are we looking for?
No choices are offered. My teacher said "called after" but I find this phrase makes no senses. I think she mistook for "named after" or maybe she mistyped the sentence.

• These are sold ___ five selling each.

I would fill with "by". But my teacher fills with "at". She says that selling is an monetary unit like $. Yet, I have never known any monetary unit called selling

These are sold by the bushel / kilo / dozen
These are sold at five shillings each.
These are sold at five dollars a pound. Did she write it or speak it?
She typed it for me. Perhaps she mistyped shillings into selling but she took selling for granted. What kind of English teacher is she?

linhtho0211 I have always done my duty ___ my students.
I have always done interesting things with my students.
I have always done well by my students. --> What does this sentence mean? I believe duty is included, but "above and beyond the call of duty" is also implied. Perhaps, "I've always done more for my students than might be expected of me."
I have always done my duty to my students.
I'm thinking of the Boy Scout Oath I learned as a child: "On my honor I will do my best to do my duty to God and my country, etc."

--> So you would prefer "to", right? I would. To my ear, it's the natural choice. I suspect the problem may arise because "to do my duty" may be used with or without the [prepositional phrase] complement. (Forgive me for using "complement" generically.) "I've done my duty." "I've done my duty to my wife." When you use it the first way, and then add the complement as an afterthought, you may forget that "to" is required. "I've done my duty - - - by my wife." Whereas you would not say, "My duty by my wife has been faithfully performed."

• The boy was called ___ by his grandfather.

I think the sentence means that his grandfather named the boy. I've looked up the dictionary for the phrasal verb of call meaning as name but found nothing.
I don't think so. Children are usually named by their parents, and the verb is "to name." The grandfather would more likely make up a nickname for the boy. The boy was called "Sonny" by his grandfather. Are there no optional choices offered? The preposition "by" is already there! What kind of word are we looking for?
No choices are offered. My teacher said "called after" but I find this phrase makes no senses. I think she mistook for "named after" or maybe she mistyped the sentence. Okay. I'm now seeing this in a different light. She's correct. (I guess we (I) instinctively think of the preposition as coming first.) When someone is leaving the scene, you sometimes "call after him" to remind him of something, or to give him some brief additional bit of information. The construction is similar to "The boy was spoken to by his grandfather." This one means that his grandfather "gave him a lecture." IMHO "spoken to" and "called after" may be considered as "fixed expressions," and can give us the strange "two prepositions in a row" situation.
"The boy was named after his grandfather" is also possible, but the "by" would be strange indeed. You could say he was named after his grandfather by his parents, but you wouldn't say "He was named after his grandfather by his grandfather." To express something like this, you might say, "The grandfather named the boy after himself."

The passive voice always makes these games more interesting. If you render it in active voice, the expression seems more natural, because you don't have to deal with the double preposition. "The grandfather called after the boy, reminding him he had an appointment with the dentist after school."

You could also say, in the passive, "The boy was called back by his grandfather," but I believe "back" is an adverb here, and not a preposition. But in active voice, "called back" would probably be interrupted by the indirect object: "His grandfather called him back." (Edit. Shoot! I think that's the direct object!)

These are sold ___ five selling each.
I would fill with "by". But my teacher fills with "at". She says that selling is an monetary unit like $. Yet, I have never known any monetary unit called selling

These are sold by the bushel / kilo / dozen
These are sold at five shillings each.
These are sold at five dollars a pound. Did she write it or speak it?
She typed it for me. Perhaps she mistyped shillings into selling but she took selling for granted. What kind of English teacher is she? Typical.