Giải đáp thắc mắc của bạn.

change into neg (-) and inter (?) from:
1. we are going to visit the citadel next sunday
(-)
(?)
2. tom goes to the library every friday.
(-)
(?)
3. we have been here since 6 o'clock.

(-)

(?)
4. the children are playing in the yard.
(-)

(?)