单项选择题
A．their brains could not function efficiently any more B．the full development of both sides of their brain was achieved C．their bodies stopped working D．they were very old
A．Too expensive. B．Hard to drive. C．Easy to control. D．More than just a charg
A．when one man feels happy, another man will feel sad B．what will make one man happy may make another man happy also C．different people hold different opinions about happiness D．both A and B