听力里面的句子:And how strong is the evidence that climate change is happening that it's really something we need to be worried about?请问happening后面的that引导的是什么从句?
This is the question about which we've had so much discussion这句话中为什么要有个介词about?Everything that he said seemed quite reasonable这句话中为什么又没有介词了?介词什么时候,用什么时候不用??