但是又经过27个月后，幸存的感染艾滋病的儿童中只有一半的抗体浓度维持在有效水平，而健康儿童的数字几乎是90%。

But after a further 27 months, only half of the surviving HIV-infected children maintained antibody levels high enough to protect against measles, versus almost 90 per cent of healthy children.

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相比之下，夏洛特的贫困儿童中，跻身上层的人仅有4.4%；而底特律这一数字为5.5%。

By contrast, just 4.4 percent of poor kids in Charlotte moved up to the top; in Detroit the figure was 5.5 percent.

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儿童掌握数字词汇的概念需要付出很大的努力。

It takes great efforts for children to grasp the concept of number words.

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