As a result, the total population was divided into four groups: control (44), low exposure (48), middle exposure (48) and high exposure (48).

因此所调查人群分为四组，其中对照组44人，低暴露组48人，中暴露组48人，高暴露组48人。

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The notion that Africa's emerging middle classes need more exposure and more encouragement is entirely correct.

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He saw in the Alpha course a way to draw in the young middle classes whose only exposure to the Gospel came at school and smart weddings.

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They also need to be firm that innovative private sector solutions like Public Private Partnerships and other fully private sector-based investments must be advanced to drastically reduce the exposure of particularly middle income Americans from the high costs of these projects.

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