Believer wrote:

In regard to No.2,  I can almost swear that I have heard some English professionals saying that there is an implicit word "to" there and whenever you hear the sentences without it, just remember it is to be included for a sentence to be a correct sentence.

While I recognize that some people will make this claim, I contend that it is counter productive to rely on the implicit existence of the word to.

The indirect object is not native to Indo-European languages. In the simplest scenario of their usage, these nouns had to be marked because word order alone was insufficient to identify the function of such nouns within the clause. With the evolution of English to the use of prepositions, the indirect object marker evolved in two distinct manners. When the direct object follows the verb and the indirect object is last, the earlier usage, the indirect object must be marked with a preposition, and to was selected for this purpose. When the indirect object follows the verb and the direct object is last, the newer usage, word order alone is sufficient to mark the function of the indirect object and no preposition is required.

I consider that it is not useful to get hung up on an arbitrary marker of the indirect object, the preposition to, and to believe that without its presence we must somehow devolve to the recognition that it must be there because it is required under other conditions.