Which statement applies to both senators and representatives
a they serve four-year terms.
b they can be expelled for breaking rules.
c they must have a college education.
d they should be registered voters.

I believe the answer is: B. They can be expelled for breaking rules.

The expellation process is regulated through The United States Constitution (Article 1, Section 5).
To be subjected for expellation, the senators and the representative must be proven to have broken the rules after undergoing a through investigative process. After that, the expellation need to be voted for more than 2/3 of the members