Which of the Following Best Explains Why a Certain Amount

Which of the following best explains why a certain amount of unemployment may be socially desirable?

A) A pool of unemployed workers drives down the average wage in the economy, and keeps workers from becoming greedy.
B) A pool of unemployed workers provides an incentive to those employed to remain productive.
C) Unemployed workers have the time to upgrade their skills and training.
D) When some workers become unemployed it provides a chance to others in the labour force to become employed.
E) The time spent unemployed by the worker is valuable for finding the most appropriate match with firms.