Given:
In parallelogram ABCD, two of its vertices are A(-4,0) and B(0,3).
To find:
The equation that represents a line that contain CD. 
Solution:
We have,
A(-4,0) and B(0,3)
Slope of AB is 



The slope of line AB is 
 .
.
Opposite sides of a parallelogram are parallel and slopes of parallel lines are equal.
In parallelogram ABCD, AB and CD are opposite sides. So, their slopes must be equal.
Slope of line AB = Slope of line CD = 

The slope intercept form of a line is

Where, m is slope and b is y-intercept.
Slope of line CD is 
 , it means the line must be of the form
, it means the line must be of the form

Coefficient of x is 
 only in option a.
 only in option a.
Therefore, the correct option is a.