题目

About ________ of his spare time ________ spent in reading. A . third-fifths; are B . three-fifths; is C . three-fives; are D . three-fifth; is 答案：B心脏能将血液泵至全身并保证按一定方向流动，不会倒流。下列叙述错误的是 [     ]A．心脏的肌肉发达B．动脉里有动脉瓣C．心房和心室间有房室瓣D．心室和动脉间有动脉瓣