Empirical study of u. s. house elections has shown that gerrymandering:

a) bias exists but has decreased since the 1960s

b) bias exists and has increased since the 1960s

c) does not affect election outcomes

d) does not change the voting behavior of representatives

e) does not exist and never has

'D' and 'E' are definitely not good answers. You can't measure 'bias', so 'A' and 'B' are out of the question. Best answer is C. Because Biased people can change the outcome but gerrymandering is manipulating boundaries.

Do not hold me against this answer, this is just my opinion, hope this helps or affects your insight in a positive way.

Gerrymandering- "Basically, gerrymandering is a process in which the people running in the elections gets to chose there number of voters in a particular region."

Explanation:

As there are some states in which the number of voters for a specific party and candidate are analyzed for a long time. Which makes it easy for candidate and the party to predict and most of time win the elections in that  region.As it makes it more easy for the party in power to maintain there number of seats and more over some times makes them in a position to win it again.As option (b) is the best one choose from.

This link explains it