The problem is difficult but he worked it out.A finally B final C last

问题补充：

The problem is difficult, but he worked it out.

A、finally B、final C、last

答案：

解析：根据语境可知此句的含义是这个问题有难度，但最后他还是做了出来。此题考查最后在英语中怎样表达。有三个短语或单词表示词义，in the end，at last，和finally，根据选择项的提示可知B是形容词，C表示上一个，故选择A。