#### Answer

a. nonlinear
b. linear
c. nonlinear
d.linear

#### Work Step by Step

A key note when finding if a graph is linear or not is if it's a line or dots creating a line, it is linear.
So,
a. the graph is not a straight line so it is nonlinear.
b. the graph is a straight line so it is linear
c. the graph makes a U shape and is not a line so it is nonlinear.
d. The dots in the graph forms a staright line so it is linear.