. . . . . . birds, can we fly?

Answer: Option B

The correct answer is B: Like.

Let's understand why:

The sentence needs to compare ourselves to birds.

A: Before - This word refers to time and doesn't make sense in the sentence.
Example: Before eating, wash your hands.

B: Like - This word is used to make a comparison. "Like birds" means similar to birds. This fits the sentence perfectly.
Example: He runs like a cheetah.

C: As - While "as" can also be used for comparison, it needs more structure in the sentence (like "as birds do"). Simply "As birds" is grammatically incorrect in this context.
Example: Do as I say.

D: Without - This word means lacking something, which doesn't fit the comparison needed.
Example: Without water, we cannot survive.

So, the complete and correct sentence is: Like birds, can we fly? which means, "similar to how birds fly, can we also fly?"