I think I should work ____(hard) at English填hard还是harder?

I think I should work ____(hard) at English填hard还是harder? I don't work hard at English because I think it's______ I think you should work hard 变同义句 hard at work school I(? I work hard at school. I work hard at school.So ____(do)my brother I often dream ---- hard work at night .填介词 I think it hard to learn English well if we don't work hard i think [ ] hard to learn english well if we don't work hard At work,I must work hard work hard in还是work hard at? We should work hard at english语法正确吗