What is the difference between unemployment and underemployment?

a$)$ Unemployed individuals are actively seeking work, while underemployed individuals are not.

b$)$ Unemployed individuals have no job, while underemployed individuals are working part$-$time when they would prefer full$-$time work.

c$)$ There is no difference, they are the same.

d$)$ Unemployed individuals receive benefits, while under??