Fill in each blank a suitable word

1.____________is a force which pulls things toward the center of the Earth. 
Direction
Friction
Gravity
Lean
2.When people have a problem, they need to find out a __________ to fix it. 
imagination
solution
idea
invention
3.______________ force keeps a body moving along a circular path.
Normal
Centripetal
Friction
Magnetism 
4."Do you need any help? "   - "_____________"
I'm busy.
You are welcome.
No, thanks.
I'm afraid I can't.
giúp nhank nhak
ak mak chỉ cần ghi đáp án thou nhak