问题
单项选择题
A．The heart pumps blood in two directions,
B．The blood is circulated round the body in one direction only by the pumping action of the heart.
C．The blood moved with a backward and forward motion.
D．The heart pumps blood in all directions.
答案
参考答案：B
解析：[听力原文]What did William Harvey find out in 1628 [详细解答] 文中可以听到：He found out that the blood is circulated round the body in one direction only by the pumping action of the heart．由此可选B。