1. Cấu trúc: (+) S + am/ is/ are + Ving The children are playing football now. (-) S + am/ is/ are + not + Ving The children are not playing football now. (?) (Wh-) ...
1.Công thức (+): S + had + been + V-ing (-): S + had + not + been + V-ing (?): Had + S + been + V-ing? Ví dụ: (+): It had been raining very hard for two hours before ...