As a series of compressions and rarefactions... hope it helps :)
Answer:

Explanation:
The gravitational force between two objects is given by

where
G is the gravitational constant
m1, m2 are the two masses
r is the separation between the two masses
In this problem, we have
the mass of each truck
r = 2.0 m is their separation
Substituting,

The more it is Red shifted.
This property is called "Opacity".
The question is worded in a difficult way. A more easily understood wording of this question would be:
"<em>What is the name of the property of a material that prevents light passing through?"</em>