We're using the correlative not only X but also Y
So, we need to ensure that X and Y have parallel structure.

The prime lending rate is a key rate in the economy: not only are the interest rates on most loans to small and medium-sized businesses tied to the prime, but also on a growing number of consumer loans, including home equity loans.

(A) not only are the interest rates on most loans to small and medium-sized businesses tied to the prime, but also on (not parallel)


(B) tied to the prime are the interest rates not only on most loans to small and medium-sized businesses, but also on (parallel)


(C) the interest rates not only on most loans to small and medium-sized businesses are tied to the prime, but also ??? (not parallel)


(D) not only the interest rates on most loans to small and medium-sized businesses are tied to the prime, but also on (not parallel)


(E) the interest rates are tied to the prime, not only on most loans to small and medium-sized businesses, but also ?? [needs "on"] (not parallel)

Answer = B

Cheers,
Brent