the bus would not have had to take the

Question

A
long detour instead of the main
B
highway if the bridge did not become
C
treacherous in the aftermath of an ice
D
storm.

why is C wrong?

thanks so much !

Answer 1

C. did not become

Answer 2

would not had to take if the bridge had not become

verb tense

Answer 3

You can read and study verb tenses, specifically the sequence of tenses here:

http://grammar.ccc.commnet.edu/grammar/verbs.htm#sequence