Ai giải giúp mình
1. My grandfather _____________ (die) after he _______________ (be) ill for a long time.
2. Mary _______________ (burn) her hand when she __________________ (cook) dinner.
3. While we _________________ (cross) the street, the policeman _______________ (shout) at us.
4. While I __________________ (walk) around the park, I ____________ (see) Mr. Smith.
5. As he _______________ (drive) on a highway, he met a terrible accident.
6. Tom is cleaning the floor while his mother ______________ (cook) dinner.