楼上bluwave答得最好.我就以他的为基础点评一下.
1."If the temperature went up,the water would evaporate."
注意water前面要加定冠词(其他几位都忘了加).其实这句不需要用虚拟语气：
If the temperature rises,the water will evaporate.
If the temperature goes up,the water will evaporate.
2."You say that you can come.That is great.If you came tomorrow,you would see Mr.Smith then."
这里虚拟语气用错地方了.第一句应该用过去时.后面的条件状语从句应该用一般现在时,主句用将来时：
You said that you could come tomorrow.That is great.If you come tomorrow,you will see Mr.Smith.
3."Tim can't come tonight.If he were able to come,we would discuss the question together."
这句不错,可以更简练,改成：
Tim cannot come tonight.If he could come,we would discuss the question together.
4."If he were in the room,he would never feel cold."
把never改成not.原句没有"从来不"的意思.
5."If you had come yesterday,you would also have got an gift."
过去完成时用gotten比较好.另外gift前面要用a,不是an.
