It is time that 为什么用过去式啊?It is the first time .为什么用完成时?我总记不住

It is time that 为什么用过去式啊?It is the first time .为什么用完成时?我总记不住 it is the first time that后为什么用完成时 it is the first time that I -have come to BeiJin为什么要用完成时啊,后面 请问：1,the first time 是不是可以是连词；2,it is the first time 是不是要用完成时 This/It is the first/second time＋that从句,that从句谓语为什么要用现在完成时 SOS1.It is the first time .that .：某人第一次做某事,那that 后是不是定要用完成时． 为什么it is time后动词可以用过去式? it is time 过去式 为什么“this is the first time i have baked it"为什么后面用现在完成时? it is the first time that i ()here it is the first/second.time that+现在完成时 it is the first time that是主语从句吗