If you are under $20,$ you cannot be eligible for insurance. If your age is between $20$ and $35,$ you will receive a $15\%$ discount. Anyone above $35$ is not eligible for the discount. Which of the following test inputs cover all the equivalence classes?

a$.$

$17,25,36$

b$.$

$18,20,35$

c$.$

$19,22,40$

d$.$

$18,25,36$