what I can do is studying hard正确吗

what I can do is studying hard正确吗 What I can do is to keep working hard为什么要用what啊? What I must do is study hard. 句子what I can do is to study hard.为什么要有to? what i need to do what i can to do?语法正确吗? all what i should do is to study hard.请问all what i should do I do what i promised no matter how hard it is All i need is I am very hard to do I can do is hope that "you" c what can I do what must I do正确吗 i do what i promised no matter how hard it is. Can you do what I can do?