I warned him . . . . . . . . his learning. A. of B. from C. for D. from

The correct answer is A. of.

The preposition “of” is used to indicate the object of a warning. In this case, the warning is about the person’s learning.

The other options are incorrect because they do not make sense in the context of the sentence.

• The preposition “from” is used to indicate the source of a warning. In this case, the warning is not coming from anything, but is being given by the speaker.
• The preposition “for” is used to indicate the purpose of a warning. In this case, the purpose of the warning is not to achieve anything, but is simply to inform the person about the danger.
• The preposition “to” is used to indicate the recipient of a warning. In this case, the recipient of the warning is the person who is being warned.

I hope this explanation is helpful. Let me know if you have any other questions.