下列选项中，存在互相监督关系的是（    ）

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    The skin is ____ essential part of your body and its ____ organ. You have three ____ of skin which act as a barrier ____ disease, poisons and the sun's harmful rays. The ____ of your skin are also very ____: it keeps you warm or cool; it prevents your body from ____ too much water; it is where you feel cold, heat or pain it gives you your sense of ____. So you can imagine, if your skin gets ____ it can be very serious. First aid is a very important first step in the ____ of burns.

被称为“地球之肺”的是：

下列现象中，属于生物因素影响的是（  ）