Compared with 2 million tons last year our coal output has increased three times; that is

问题补充：

Compared with 2 million tons last year, our coal output has increased

three times; that is to say, our coal output has increased8 million tons

this year.

A. to; to

B. to; by

C. by; by

D. by; to

答案：

A. to; to

B. to; by

C. by; by

(答案→)D. by; to

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