Sentence Correction (SC) | In 1980 the United States exported twice as much of its

In 1980 the United States exported twice as much of its national output of goods as they had in 1970.
(A) twice as much of its national output of goods as they had
(B) double the amount of their national output of goods as they did
(C) twice as much of its national output of goods as it did
(D) double the amount of its national output of goods as it has
(E) twice as much of their national output of goods as they had