【单选题】

If you’re relying on Grandma to help with child care, it’s time to reconsider.

A、new study of more than 54 000 women found that those who watched their grandkids 9 hours a week or more were 55% more likely to have a heart attack. These women may have less time to take care of their own health, says lead author Sunmin Lee, ScD, of the Harvard School of Public Health. Younger kids may pose more risk because they need more care.
"However willing your mom might seem, it’s up to you to figure out how much she can really handle," says Meredith Minkler,DrPH, a public-health professor at the University ofCalifornia,Berkeley, and an expert on grandparents as caregivers. "It’s not just about physical health. Older adults need time to connect with people of their own age. Social isolation is a major risk factor for illness." If your mom helps out, make sure she has breaks during the day, as well as "vacations" at regular intervals.
Young people should be careful asking their parents to help with child care because ______.
A、it is risky for their children
B．it is hard job for old people
C．they don’t know how
D．it’s not good for their health