Which of the following is not a complete sentence

Question

A: Assembling the bookcase, as my father mentioned.

B: While assembling the bookcase, my father fell asleep.

C: My father assembled the new bookcase in one day.

D: My father has assembled the bookcase.

Answer 1

And you think it's ... ??

Answer 2

Which doesn't seem to be a complete thought?

Answer 3

Yes. A is not complete.