—I bought this shirt for 35 yuan yesterday. —It’s on sale today for only 29. You should ha

问题补充：

—I bought this shirt for 35 yuan yesterday.

—It’s on sale today for only 29. You should have waited.

—Oh, really? But how I know?

A. would

B. can

C. did

D. do

答案：

A. would

B. can

(答案→)C. did

D. do

解析：因为意思是“我当时 (昨天) 怎么知道呢？”。