单项选择题A．Men blush more than women. B．Children blush easily. C．People blush consciously. D．It is more or less a learned behavior.

单项选择题A．Because the police could not see them in the dark. B．Because many of them were armed with guns. C．Because there were not enough policemen to catch them all. D．Because they were hidden inside big buildings.

单项选择题A．It was by continuous exploitation of the environment. B．It was largely by chance. C．It was because of houseflies. D．It was by chance initially and by cleverness now.

单项选择题A．They suffer from mental pains. B．They start doing something in an active way. C．They become uninterested in class activities. D．They may grow up to be passive watchers.

单项选择题A．They have three children already. B．Cathy wishes to have a baby, but Tom doesn’t. C．They will start a family as soon as they get married. D．They don’t want children for the time being.