We’ve a lot of things to do. But we must get some sleep.A. at firstB. at onceC. first of

问题补充：

We’ve a lot of things to do. But we must get some sleep.

A. at first

B. at once

C. first of all

D. the first thing

答案：

A. at first

B. at once

(答案→)C. first of all

D. the first thing

解析：first of all= first 首先； at first= in the beginning最初。