Helen had left her keys in the office so she had to wait unt

这里要选的时态,主要看she had to wait 的时态,这里用了一般过去时,所以后半句也用一般过去时。同样如果只有后半句的话,也应用came。一般情况下 由until引出的重句,前后都是一般现在时或都一般过去时用的较多,但也可以是前半名是将来时后半句是一般现在时；也可以是前半句是一般现在时,后半句是现在完成时。例1：First write them down in your exercise books, then practice them orally until you have learned all of them by heart。例2：I will stay with you until your lesson begins