“when+过去分词”中的过去分词通常应视为被动语态的省略，而不能视为完成时态的省略。如：

When (it is) heated, ice will be changed into water. 当冰受热时，它就会变成水。

Metal expand when (it is) heated and contract when (it is) cooled. 金属热则膨胀冷则收缩。

It will seem as nothing when (it is) compared with his action. 和他的行为相比，这似乎是微不足道的。

The author was able to give his book a plug when (he was) interviewed on a talk show. 作者在接受访谈时可以给自己的书做一番广告。

When (you are) asked for your views about your current job, on no account must you be negative. 当你被问及对目前工作的看法时，绝不要流露出消极情绪。