Sentences that use the phrase "twice" vs. "double" throw me off...can anyone explain how to dermine the correct use of "twice"/"double" and what/why the correct choices are in the two sentences below:

1 In 1980 the United States exported twice as much of its national output of goods as they had in 1970.
a.
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

2. Today, because of improvements in agricultural technology, the same amount of acreage produces double the apples that it has in 1910.
a.
b. twice as many apples as it did
c. as much as twice the apples it has
d. two times as many apples as there were
e. a doubling of the apples that it did


Thanks!