My sister is good . . . . . . . . French. A. at B. with C. on D. in

The correct answer is D. in.

The word “in” is used to indicate a location or position. In this case, the speaker is saying that their sister is good in French. This means that their sister is proficient in the French language.

The other options are not as accurate. The word “at” is used to indicate a specific point in time or space. The word “with” is used to indicate a relationship or association. The word “on” is used to indicate a surface or support.

Here are some examples of how the other options could be used in a sentence:

• My sister is good at math.
• My sister is good with children.
• My sister is good on the piano.