As it turned out to be a problem of no importance we so much time looking into it . A. n

问题补充：

As it turned out to be a problem of no importance , we so much time looking into it .

A. needn’t spend

B. didn’t have to spend

C. needn’t have spent

D. oughtn’t to spend

答案：

A. needn’t spend

B. didn’t have to spend

(答案→)C. needn’t have spent

D. oughtn’t to spend

解析：句意：因为结果证明这是个不重要的问题，我们本不必花这么多的时间调查它。从这句话的一般过去时态，可以判断AD是错的，B项是过去不必做，是表示事实，而这里表示的是虚拟语气，本不必做而做了，用needn’t have done，选C。