1. It is a week since he came here last time.2.How long hasn't he come here? 第三人称要用has ,要用现在完成时。3. How many days hasn't he come here ?这种说法是对的，for在疑问句时就省略了。...
1. 同义句：He has disappeared for a week2. It is... since只是说since后面的从句不能用否定I haven't seen him since 3 years ago （正确）It has been 3 years since he hasn't come here （错误）3. 完成时不能接瞬...
