doing
have trouble doing sth.Alex Steward studies （ ）than his brother A more hardly B more hard C more harder D harder会吗 理由Dhard本身就是副词, 比较急harder, 更努力为什么 more hard不行没听说过用more hard除非说有更多艰难的事要做more hard work to do, 这里more也是形容work的说更努力，用hardertry harderstudy harderwork harder