问题补充：
An early typewriter produced letters quickly and neatly; the typist, couldn see his work on his machine.
A. however
B. therefore
C. yet
D. although
答案：
A. however
B. therefore
C. yet
D. although
解析：
however 然而。
本题译文：早期的打字机打起字来又快又整齐, 然而打字员不能看着机器键盘打字。a
