D) she took pictures of her classmates. This is the correct option.
The speaker was making her yearbook. She wanted a picture of her class mates at the homeroom. When they saw her taking a picture of them, they jut made goofy faces - they must have put funny faces - at the camera.
These options are not right:
-A) she made fun of her classmates. ( He classmates put funny faces at the speaker's camera. The speaker did not laugh at them).
B) she asked her classmates to smile. ( The speaker did not give the classmates any instructions. She just caught them off guard with her camera).
C) she felt her classmates were silly. ( She did not give any opinion about her mates).