19. There is no point ____________the piano unless you practise every day.
A. to learn to play
B. in leaning to play
C. by learning to play
D. having learned to play
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We didn't go shopping yesterday because it ____________ all day.
A. had rained
B. would rain
C. was raining
D. has been raining
汽车的低压导线采用单股线。()
A. 对
B. 错
汽车的低压导线采用多股线。()
A. 对
B. 错