Everyone knows that regular bedtimes are important, especially for children. But a research by Yvonne Kelly of University College, London, shows that daughters, it seems, do benefit from regular bedtimes. Sons do not. Dr Kelly and a team of colleagues examined the bedtimes and cognitive  abilities of 11,178 children born in Britain between September 2000 and January 2002, who took part in a research project called the Millennium Cohort Study. The bedtime information they used was collected during four visits interviewers made to the homes of those participating in the study. These happened when the children were nine months, three years, five years and seven years of age. Besides asking whether the children had set bedtimes on weekdays and if they always, usually, sometimes or never made them, interviewers collected information about family routines, economic circumstances and other matters--including whether children were read to before they went to sleep and whether they had a television in their bedroom. The children in question were also asked, at the ages of three, five and seven, to take standardised reading, mathematical tests, from which their IQs could be tested. Dr Kelly's report shows that by the time children had reached the age of seven, not having had a regular bedtime did seem to affect their cognition. But that was true only if they were female. On the IQ scale, whose average value is 100 points, girls who had had regular bedtimes scored between eight and nine points more than those who did not. Boys were not completely unaffected. Irregular bedtimes left their IQs about six points below those of their contemporaries at the age of three. But the distinction disappeared by the time they were seven. This difference between the sexes is puzzling. "I did not expect it, and more research is necessary." said Dr Kelly. How long did the research last?
At least nine months Nearly three years Less than five years About seven years
Question: Everyone knows that regular bedtimes are important, especially for children. But a research by Yvonne Kelly of University College, London, shows that daughters, it seems, do benefit from regular bedtimes. Sons do not. Dr Kelly and a team of colleagues examined the bedtimes and cognitive  abilities of 11,178 children born in Britain between September 2000 and January 2002, who took part in a research project called the Millennium Cohort Study. The bedtime information they used was collected during four visits interviewers made to the homes of those participating in the study. These happened when the children were nine months, three years, five years and seven years of age. Besides asking whether the children had set bedtimes on weekdays and if they always, usually, sometimes or never made them, interviewers collected information about family routines, economic circumstances and other matters--including whether children were read to before they went to sleep and whether they had a television in their bedroom. The children in question were also asked, at the ages of three, five and seven, to take standardised reading, mathematical tests, from which their IQs could be tested. Dr Kelly's report shows that by the time children had reached the age of seven, not having had a regular bedtime did seem to affect their cognition. But that was true only if they were female. On the IQ scale, whose average value is 100 points, girls who had had regular bedtimes scored between eight and nine points more than those who did not. Boys were not completely unaffected. Irregular bedtimes left their IQs about six points below those of their contemporaries at the age of three. But the distinction disappeared by the time they were seven. This difference between the sexes is puzzling. "I did not expect it, and more research is necessary." said Dr Kelly. How long did the research last?
A. At least nine months
B. Nearly three years
C. Less than five years
D. About seven years
Answer: