请问second conditional句型条件从句为什么要用过去式?

请问second conditional句型条件从句为什么要用过去式? second conditional与third conditional的区别 英语中one conditional,second conditional,third conditional 请问英文什么是时态,conditionals:zero,first,second and third conditional. conditional the first （second ）conditional clause条件句怎么还有 first second之分呢? 请问什么是unreal past conditional 和unreal present conditional?能个给出2个关于睡眠的例子吗? Present conditional first conditional Conditional offer firm acceptance conditional approval是什么意思 conditional access是什么意思 请问a second 和 the second的区别 请问a second 和 the second的区别 second second second second