第三群体是对照组，买家被简单的告知只关注他们自己的角色。

The third group was a control; the buyers were told simply to concentrate on their own role.

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在13个人口群中，7个被随机分配到1996年至2004年的3轮筛查，而另外6个（对照组）获得的是标准护理。

Of 13 population clusters, seven were randomly allocated to three rounds of screening between 1996 and 2004, while standard care was provided in six (control arm).

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结果表明，不同植物类群(禾草类、莎草类)增加降水20%，地上生物量分别比对照提高103。

The results indicated that in the grass group and sedge group, the above ground biomass in the plots, where the precipitation increased by 20%, was 103.

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One group of children was a control group; the second group was taught to think back to experience that make them laugh or smile.

一群小孩组成对照组;,有人教第二组小孩回想,让他们大笑或微笑的经历。

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