A:was coming
B:will come
C:had come
D:have come
your lessons.There' ll be an exam tomorrow.
下列装置都可制取氨气,其中药品选用错误的是( )
如图所示,用甲乙两种装置匀速提升同一重物,若每个滑轮重相同,不计摩擦及绳重,则下列说法正确的是( )