When a cold air mass replaces a warm air mass, it's called an) front.
A. Stationary
B. Warm
C. Occluded
D. Cold

Cold Front

Explanation:

Cold air mass replaces a Warm air mass, This will be a cold front.

d. the weight of the book

explanation:

the universal gravitation equation. since the gravitational force is directly proportional to the mass of both interacting objects, more massive objects will attract each other with a greater gravitational force. if the mass of one of the objects is doubled, then the force of gravity between them is doubled.