11. A higher interest rate is only one of the factors, albeit an important one, that keeps the housing market from spiraling out of control, like it did earlier in the decade.

a that keeps the housing market from spiraling out of control, like it did earlier in the decade.
b that keep the housing market from spiraling out of control, as it did earlier in the decade
c· that keeps the housing market from spiraling out of control, as it did earlier in the decade
d· that keep the housing market from spiraling out of control, like earlier in the decade
e· that keep the housing market from spiraling out of control, like it did earlier in the decade

why is the correct answer b. what is the subject .. a higher intrest rate or factors.