When_______,waterwillbeturnedintosteam.
A
水被加热时会变成蒸汽。因为主句主语 water 和从句谓语 heat 的关系是被动的，所以用过去分词。
Neverbefore_______sorapidlydevelopingasitistoday．
Sincewehaveafocusedsubject，weshouldnottalk________.
The farming methods have been ________ improved with the invention of the new machine.
During the past two decades, research has ________ our knowledge of daydreaming.