单项选择题
A．They both attract scientists attention. B．They can both be quite challenging. C．They are both thought-provoking. D．They may both lead to surprising findings.
A．It is more exciting than space e travel. B．It is much cheaper than space travel. C．It is much safer than space travel. D．It is less time-consuming than space travel.
A．They grow up to be funny and charming. B．They often have a poor sense of direction. C．They get less attention from their parents. D．They tend to be smart and strong-willed.