Are my answers correct?

Question

Identify each energy exchange as primarily heat or work and determine weather the sign of ?E is positive or negative for the system.

A. A rolling billiard ball collides with another billiard ball. The first ball (system) stops rolling after the collision.
My answer= Work and ?E is negative for the system.

B. A book is dropped to the floor.(The book is the system).
My answer= work and ?E is negative

C. A father pushed his daughter on a swing. (the daughter and the swing are the system)
My answer= work and ?E is positive

Thanks!