Helen and Bob are working hard these days because they will put ______ a short play in the school Talent(才艺) show.
A:over
B:away
C:off
D:on
— Yes, he does.
有一种电子牙刷,它能发出超声波,直达牙刷棕毛刷不到的地方,这样刷牙既干净又舒服.关于电子牙刷,正确的说法是( )