单选题 The early typewriters produced letters quickly and neatly; the typists, ______ couldn't see their work on their machine.

A. however
B. therefore
C. yet
D. although

【正确答案】 A

【答案解析】[解析] 本题考查逻辑关系。 [解析] however adv. 然而，不过，无论如何；therefore adv. 因此，因为，由此可得；yet conj. 然而，但是；although conj. 尽管，虽然，然而，但是。判断句意可知，此处应该为转折关系。A、C、D都可以表示转折，但是只有however的词性符合要求。故答案为A。