---Why do you come back so late?-Because there were too many people in the supermarket

问题补充：

---Why do you come back so late?

---Because there were too many people in the supermarket, and I had to to pay for the things.

A. wait in line

B. cut in line

C. stand up

D. speak loudly

答案：

(答案→)A. wait in line

B. cut in line

C. stand up

D. speak loudly

解析：考查固定短语。句意：----你为什么来的如此晚？----因为超市里有太多人，我不得不排队等候来付钱。故选A。