题目

世界各大洲中，平均人口自然增长率最高的洲是(     )        A．亚洲            B．非洲           C．大洋洲             D．南美洲 答案：B．It is hard to say what kind of person he is. Sometimes he is very friendly;  at other times he ___ be very cold. [     ]A. canB. must C. willD. shall