It will cost a lot of time. I think we shall need it and it will certainly be useful to us

问题补充：

It will cost a lot of time. I think we shall need it and it will certainly be useful to us more or less.

A. What’s more

B. As a result

C. On the other hand

D. After all

答案：

A. What’s more

B. As a result

(答案→)C. On the other hand

D. After all

解析：A而且（表示递进关系）；B结果是；C另外一方面；D终究，毕竟；句义：这的确要花很多的时间，但另外一方面，我认为我需要它，它或多或少地对我们有帮助。根据句义说明on the other hand表示上下文之间的轻微的转折，符合上下文的含义。故C正确。