Ask someone else to drive you home, do not drive under the influence.
Answer:
Look<em><u> before you leap</u></em>.
Explanation:
Typically, the subordinate clause begins with an adverb.
You could also write the sentences this way:
Before you leap, look. (Note the necessary comma.)
B because the reader already knows what is about to happen to the characters while the others run in chronological order
This builds tension rather than shock as it would if it were in chronological order