既能增强神经肌肉兴奋性，又能降低心肌兴奋性的离子是
A．钙离子
B．镁离子
C．氢离子
D．氢氧根离子
E．钾离子
参考答案：E
运动系统由骨、骨连接和骨骼肌构成，在运动中起着杠杆作用的是______，骨骼肌收缩使骨绕着关节活动，所以骨骼肌在运动中起着______的作用，它的收缩受______的协调和控制．
During job interviews, many graduates use the reputation of their schools to the full _____ themselves
to the employers. [ ]
A. presented
B. being presented
C. to present
D. having presented
