单项选择题To solve the present social problems the author suggests that we should______.
单项选择题From the passage we can infer that real happiness of life belongs to ______.
单项选择题On the basis of their models, scientists are of the opinion that______.
单项选择题A concentration of carbon dioxide in the atmosphere would______.
单项选择题Although the fuel consumption is greater in the northern hemisphere, temperatures there seem to be falling. This is ______.