For which values of $r$ is the function $y=t^r$ a solution of $t^2{y}^{\text{'}\text{'}}-5t{y}^{\text{'}}+8y=0$

Select one:

a$.$

$r=-2,-4$

b$.$

$r=2,3$

c$.$

$r=2,4$

d$.$

$r=3,4$