She is standing . . . . . . . . her boyfriend. A. for B. by C. in D. with

The correct answer is: with.

The preposition “with” is used to indicate that someone is in the company of another person. In this case, the woman is standing with her boyfriend.

The other prepositions could be used in different contexts. For example, the preposition “for” could be used to indicate that the woman is standing in support

of her boyfriend. The preposition “by” could be used to indicate that the woman is standing next to her boyfriend. The preposition “in” could be used to indicate that the woman is standing inside a group that includes her boyfriend.

However, in the context of the question, the preposition “with” is the most likely choice.