答案：B

题目分析：句意：他什么时候愿意借给朋友一些钱呢？只有在他受的压力足够大的时候。回答为省略句，原句应为He is willing to lend his friends some money when he is pressed hard enough. 因主句和从句主语一致，且从句谓语动词是be动词，所以从句中的主语和be动词可省略。故选B。