The two groups of children have quite different characteristics.

这两组儿童具有截然不同的特点。

《牛津词典》

It should be noted that the two groups of children had been carefully matched by the investigators so that they were comparable in age, ethnicity, race, and social class.

值得注意的是，调查人员对这两组儿童进行了仔细的比对，以便他们在年龄、民族、种族和社会阶层方面具有可比性。

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Recently, for example, psychologists at Yale University showed a cartoon to two groups of children.

例如，最近耶鲁大学的心理学家向两组孩子展示同一组漫画。

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If vaccine supplies are limited, then the committee says two groups of children should be vaccinated before other children.

VOA: special.2009.08.05

Researchers in Glasgow compared two groups of nursery school children - some who took regular active play sessions and others who did not.

BBC: NEWS | UK | Scotland | Glasgow and West | Child obesity solution not simple

The study, led by first author Peter Ducharme, MSW, a clinical social worker at Boston Children's, compared two groups of 9- to 17-year-old children admitted to the hospital's Psychiatry Inpatient Service who had high levels of anger.

ENGADGET: Researchers create video game that monitors heart rate to keep children's anger in check

One of its directors, Professor Bob Stone, said the idea was the program would be used by groups of eight children at a time, with two taking the controls and the others making notes and discussing what to do.

BBC: News | Education | Pupils become virtual crime fighters