We’ve failed three times in the experiment so we’ll have to do ittime.A. fourB. a fourthC.

问题补充：

We’ve failed three times in the experiment,so we’ll have to do ittime.

A. four

B. a fourth

C. fourth

D. the fourth

答案：

A. four

(答案→)B. a fourth

C. fourth

D. the fourth

解析：此题考查序数词的用法。一般来说，定冠词+序数词表示顺序，而不定冠词+序数词表示“又一次”。