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。
Iunderstoodfromherthatyouundertookotherimportantwork______.
Peoplewhocan’t_______betweencolorsaresaidtobecolor-blind.
Theoutlineofrooftopsandchimneys________againstthepalesky.