Answer:
The correct answer is option a. "Its members have six-year terms, with one-third of the total members up for re-election every two years".
Explanation:
According to the Constitution, the Senate shall be composed of two Senators from each state. The members of the Senate serve a term of office is six year long and the elections are staggered over even years. Therefore only about one-third of the members are up for reelection during any election, elected on even years or every two years.