为什么第7题用when而不用if?

为什么第7题用when而不用if? 为什么If you were me、me用宾格而不用:I When you're invited for 7:00中,为什么用for而不用at? 英语为什么不用when 为什么要说If I were a fairy,而不用If I am a fairy? 为什么用if而不用becausei buy a dictionary yesterday if i had time she will get nervous when speaking in public为什么用speaking而不用when she spoke when did he leave?when did he leave?这里为什么不用leaves而用leave呢, if you are invited for 7：00 you are supposed to arrive on time为什么用“for”而不用“at” 第一个句子为什么要用what而不用where 第二个句子为什么不用强调 were 和 wes的用法为什么在When were you born?用were而不用was为什么when was your brother born?用was而不用were 例句：1.Did Tom do his home work yesterday?When?回答：I want to know if Tom did his homework yesterday.请问回答中的为什么要过去式did而不用单数第三人称does? If winter comes,_____ spring be far behind?为什么选can,而不用will if you work hard ,you will succed为什么work后用hard,而不用hardly 在宾语从句中,为什么if 后用any,而不用some? i cannot remember if i posted the letter 为什么后面用过去式而前面不用 if you park your car in the wrong place. 这里为什么不用at而用in if i were a boy again为什么用were而不用was