My counsin is good at maths ,so there_be any trouble in his working out the problem.
A.shouldn’t B.wouldn’t C.mustn’t D.needn’t
答：A
译：我表兄弟数学很好,所以他解出这个难题应该没有什么困难的.
析：表示推测,肯定用must,否定用can't,不用mustn't,排除C
needn't表示不必,不合句意.
wouldn't表示虚拟语气.这里不用.因为没有相应的虚拟条件句.也不是隐含虚拟条件：My cousin is not good at maths,or /otherwise there wouldn't be any.
shouldn't可以表示推测.