The Voting Rights Act of 1965 passed in Congress by large majorities in part because // A) representatives hope many African Americans would...

The answer to this question is somewhat subjective.  It is
difficult to know for sure why members of Congress vote the way they do.  You should
probably look in your book or your notes to find out what answer you are expected to
give.

I would argue that B is the best answer, but an
argument can be made that C is actually right.

The Voting
Rights Act was certainly made possible by white reaction to the violence in Selma.  The
fact that Southern whites would react so violently to people who simply wanted to be
allowed to vote looked very bad to whites in the rest of the country.  As the link below
says,

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A 1965 march to Selma, Alabama, by
Dr. MARTIN
LUTHER KING JR. and other civil rights supporters to demand voting rights led
to police violence and the murder of several marchers. The Selma violence galvanized
voting rights supporters in
Congress.

However, it is also
generally argued that many people supported civil rights and other legislation because
they saw it as something that JFK would have wanted.  However, I would argue that, by
1965, the Selma violence was much more fresh in people's minds and more of a factor in
creating support for this law.