Which sentence below best expresses the essential information in the highlighted sentence
A.A century ago, health professionals did not experience sleep deprivation; however, now it is a part of their jobs.
B.It is difficult to understand why health professionals have not studied the consequences of sleep deprivation.
C.Sleep deprivation used to affect only certain professions, but now it occurs in all sectors of the working population.
D.Health professionals have just started to understand that sleep deprivation in workers is a serious problem.