''The employees whined about their low wages'' is the statement that contains bias.
A biased statement refers to a statement which asserts lacking real proof for evidence that something is out of the ordinary. According to this definition, the only possible option to be a bias is option c, since the other ones contain factual information, or are statements, But regarding option c, we are not either sure or informed whether or not the employees' wages are really low as stated.
answer a and c are both facts, and answer d is a statement. answer b is biased because we are not informed whether or not the employees' wages can be considered to be low
