Aparachute works because the canvas of the parachute is acted upon by
a. inertia
b. gravity
c. velocity
d. momentum

The correct answer is a.

Explanation:

Inertia is the state of the object to resist any change in the state.

If the object is in the state of the uniform motion then it will continue in that state unless it acted by the external force.

If the object is in the state of the rest then it will continue in that state unless it acted by the external force.

A parachute works because the canvas of the parachute is acted upon by inertia. The canvas of a parachute maintains its state due to the inertia.

Therefore, the correct answer is inertia.  

d. air pressure decreases as altitude increases.