a)It's dengerous to play in the kitchen

-> It's not safe to play in the kitchen

b)My uncle often played truant when he was young

->My uncle used to play truant when he was young.

c)The post office is not far from the bookstore

->The bookstore is near the post office.

d)You should play outside instead of staying inside

->You ought to play out side instead of playing inside.

1.  It's not safe to play in the kitchen

2. My uncle used to play truant when he was young

  used to + Vnt: chỉ thói quen trong quá khứ

3. The bookstore is near the post office

4. You ought to play out side instead of playing inside

   ought to + Vnt : nói về một việc định làm nhưng lại không làm nữa.