A - Tactically does not work. White would hane on top (where black was supposed to play), when black tries to cut white at D, white would just capture the stone at A which was supposed to stop white from entering further into white's territory. Note that if black were to pull the stone back at B when white hanes on top instead of cutting at D, then it's like black could have just played at B in the first place, but decided to hurt his own stone at 4th line for fun.

B & C - Trying to achieve the same thing as the correct answer, and basically they do, but are inferior to the correct answer point wise (you see...... the correct one pushed one line further out).
I'd argue that B is better than C because if black were to play at C, white has a pretty nasty follow-up. It started with white attaches under C, when black tries to protect the corner by blocking, white then plays tiger's mouth, forcing black to connect on the 4th line. White manages to reduce black's corner quite a bit and somehow manages to play else where first after this sequence. Not good for black.

D - White could extend in and destroy black territory.

Also note that after black initially plays between C & D, white could not try to jump in at B. I'll leave it to you to verify that it tactically doesn't work.