Tom had(have)an accident when he was walking home .为什么填一般过去时,可以这样理解吗?由when引到的条件状语从句,主句用一般过去时从句用过去进行时,而when后是从句

____in the queue for half an hour,Tom suddenly realized that he had left his wallet at homea:To waitb:Have waitedc:Having waitedd:To have waited Tom had an English e ____ yesterday.补充e（） I have had an early night I an have some had 改成现在完成时 请问____in the queue for half an hour,Tom suddenly realized that he had left his wallet at home.为什么不能选have waited? (Having waited)in line for half an hour ,Tom suddenly realized that he had left his wallet at home为什么不用To have waited 而用Having waited I have had a letter from Tom.的意思? I have had a letter from tom 提问 I have had a letter from Tom.这个have had 是什么句型啊? I have had a letter for TOM 这句 have 与had from / email / Tom / I / an / have / little / got / . 排序:from,email,Tom,I,an,have,little,got. i have an american friend ----- (name) tom为什么 i have had a letter from tom .里面的had是干什么的 He has had aletter from Tom.第一个have不是助动词吗,为什么要改成had? i have an appointment with tom和i have made an appointment with tom有什么区别? i have had an X-rey为什么have后面还要用had呢?i have an X-rey不行吗? Have you had an apple 是什么时态Sam hasn't had an apple是什么时态