700. The boom in agricultural exports in the early 1970’s emptied United States grain bins and many were led to thinking that overproduction was now a problem of the past.

(A) many were led to thinking that overproduction was now

(B) many had been led to thinking of overproduction as if it were

(C) the thought this led to was that overproduction had become

(D) led many to the thought of overproduction as if it were（E）

(E) led many to think that overproduction had become

我认为become的过去时不是很好吗? 为什么要用had become 的现在完成时呢?