Answer:
For 4, a
For 5, c
Explanation for #4:
Every 2 years, a new representative for the House of Representatives (I'm going to use HOR for short) gets elected. The citizens of a state can choose a person to represent them in the HOR. Representatives can retire earlier if they want.
Explanation for #5:
A senator can serve for up to 6 years in the Senate. The elections are a bit staggered so, about 1/3 of senators are elected every 2 years. But, the answer is c, so don't get confused.
I hope this helps :D