Answer:C-cart B
Step-by-step explanation:
Given
Cart A is moving with constant speed so net acceleration is zero of the cart. So there is no force on the cart A
For cart B speed is gradually speeding up, so there is an acceleration on the cart which is the result of force.
We can say that cart B is experiencing a net force towards left.
Cart C is gradually speeding down i.e. cart C is experiencing a declaration .
So a net force towards right must be acting on cart C.
Correct answer is Cart B