单项选择题

Call it the real night shift—that nocturnal (夜间的) period when bleary-eyed adults leave warm beds to tend to the needs of sick kids, elderly parents or an ill spouse. So, who takes the night shift: Mom or Dad Women are 2.5 times as likely as men to interrupt their sleep to care for others, according to a new study by researchers from the University of Michigan. And once they’re up, women are awake longer: 44 minutes, compared with 30 minutes for men.
"People are getting up for other things, too. But more women are specifically getting up to care for dependents—that includes feeding, tending to physical or medical care, and especially for young children," says the study’s lead researcher, Sarah Burgard, an assistant professor of sociology and epidemiology at the University of Michigan School of Public Health in Ann Arbor.
Among dual-income couples with a child younger than 1, 32 percent of women reported sleep interruptions on a given 24-hour period, compared with 11 percent of men. For those with children aged 3 to 5, 3 percent of mothers and 1 percent of fathers experienced interrupted sleep. Overall, after controlling the data for differences in work commitment, partnership status and other factors, Burgard said, mothers took "the night shift of caretaking" about 2.5 times as often as fathers.
According to the study, the gender gap was the greatest during the parents’ prime childbearing and child-rearing years, their 20s and 30s—which is also the optimal period for earnings and career development. Sleep-deprived individuals do not function well on the job, Burgard said-"Poor sleep quality manifests quickly: You’re unable to focus... It’s a real limitation." Previous research into women’s lack of sufficient sleep noted problems such as undiagnosed sleep apnea (呼吸暂停症) and depression, she said, but this study sheds light on another factor: gender-defined responsibilities.
Whether the woman was the "primary caregiver, primary breadwinner, it didn’t matter," says Burgard. Among parents of children younger than 1, 28 percent of women who were the sole earner in the couple reported getting up in the middle of the night to take care of children, compared with 4 percent of men who were the sole breadwinner. "The primary care responsibilities still belong to females regardless of other obligations," says Burgard.
According to Burgard, more women get up at night to care for their children ______.