9. income inequality in the united states increased from the 1970s to the 2000s due to among other factors, tightly regulated markets depressing wages fora majority of workemb. lightly regulated markets depressing wages for unskilled workers, o c. higher-paying service obs obeo d. fewer immigrants filling fewer low-paying service jobs

I think that the best answer from the options is the following one:
B. lightly regulated markets depressing wages for unskilled workers

The thing is, unskilled workers cannot really pose  many demands for their pay, because they can be replaced by other workers. This is what has led to low wages of the unskilled workers, while increasing the wealth of the richest, who own the production means.