A、Increase the sample number. B、Extend the time of the study. C、Observe the sample group of vegetarians. D、Both A and B. D短文中提到为

A British study of how diet affects the health of new mothers and their babies produced the surprise finding that vegetarian women are more likely to have girls, one of the report’s authors said yesterday.
    In what is thought to be the first study of its kind, researchers at Nottingham University in central England found significant differences in the sex of babies born to vegetarian and meat and fish-eating women. They were examining the health conditions in vegetarian and non-vegetarian mothers, looking at things like hemoglobin levels, which show how much iron the mother has in her blood, and birth weights.
    Altogether 5,942 pregnant women were involved in the study when they were booked in Nottingham’s City Hospital during 2001. According to the researchers, vegetarian mothers were defined as pregnant women who avoided meat and fish. Nearly five percent were vegetarian among them, a total of more than 250 women.
    The birth ratio in Britain is that for every 106 boys born there are 100 girls, that’s pretty constant. In their sample group of vegetarians there were 81.5 boys born for every 100 girls.
    To further test their surprise findings, they increased the sample number to what scientists called a "statistically significant" level. The study was extended for a further six months so that the sex of more babies could be looked at. The results, covering around 150 more vegetarian women, were" just about exactly the same".
    The study also found that vegetarian mothers were less likely to smoke during pregnancy -- 10 percent did so, compared with 20 percent of meat-eaters.