Hello again, Malory.
Last night, I couldn't get one of the sentences you posted out of my mind. Rather, what I couldn't get out of my mind was the answer I gave you. So this morning I did some "research" and found out why I was feeling uncomfortable with my response.
The sentence in question is number 6.
Yesterday, I said it's a complex sentence.
According to what I've founf now, that was not wrong.
"... (for completing a large project in small sections)", can be considered a subordinate clause.
But there is another possibility: you can also consider that structure as a prepositional phrase in which the object of the preposition (what comes after it) is a gerundive phrase, not a clause. In this case, you would have a SIMPLE sentence, not a COMPLEX one.
In the case of the complex sentence, "for" would be considered within the clause itself and the whole construction would no longer be seen as a prepositional phrase. I'm not sure this last part is clear enough.
To expalin it differently, it would be similar to certain cases in which relative clauses, for example, have a preposition before the relative pronoun that introduces the clause, and that preposition is considered part of the clause:
"The house (in which I was born)."
You don't analyse "in which I was born" as a prepositional phrase in this case.
I hope that made some sense to you, and that it's not too late
Miriam