Help me please :< Which of these situations is an HR manager MOST likely to formally investigate?

A.
Employees who work the night shift complain that the kitchen is always dirty when they start work.

B.
A new hire says the explanation of pay and benefits is confusing and lacks detail.

C.
An employee says her manager gives the best assignments to people of a certain race.

D.
A manager says the members of his team don’t know very much about the benefits the company offers.