问题描述：
E-mail is very popular today .People hardly send letters ,___?A.did yhey
E-mail is very popular today .People hardly send letters ,___?A.did yhey B .do they C.didn't they D.don't they
E-mail is very popular today .People hardly send letters ,___?A.did yhey B .do they C.didn't they D.don't they
问题解答：
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