是work hard at English 还是on English?为什么

i must work hard on english.短文改错,为什么要把ON改成AT? work hard at English是什么意思 work hard with/at/in/on my English work hard () English A.in B.at C.on 是work hard at sth.还是work hard on sth. work hard on the subject,work hard at English,in your lesson I think I should work ____(hard) at English填hard还是harder? 在英语方面是On English 还是 at English You must work hard( )English.A.on B.at C.A or B work hard () English They work hard at English._____ _____ they work at English!_ (In order to master) English ,we must work hard at it为什么这样写?