it is the question that difficult to solve.
it is a question that difficult to solve
it is the question that is difficult to solve
it is a question that is difficult to solve
请问这四句话哪句正确呢?这些句子是强调句还是定语从句啊?a 和the怎么区分呢,我知道一个是特指一个是泛指,可是在这里该怎么用?还有,加不加is有什么区别呢?