What makes the Senate a continuous body?

Well supposedly unlike the White House, all of the Senate's seats are never, ever up for election, not at the same time.

Explanation:

Continuous Body: a legislative body, such as the U.S. Senate, that achieves stability by staggering the terms of its members to prevent more than a minority of seats from changing in a single election.

b.

jim crow laws were enacted in northern states.