Answer:
When using a semicolon, you connect two or more ideas.
An idea must be complete and independent. You use a semicolon only when they are all ideas.
A: Dinner is not a full idea.
is the most important part of my day. is also not a full idea.
B: After a full dinner is not a full idea.
I like to have something sweet is a full idea.
C: My favorite thing to eat is not a full idea.
is dessert is not a full idea.
D: Both ideas are complete, so that means that D is correct.