齿条升柱器是靠（）的传动使齿条带动活柱上升
参考答案：棘轮
He is considering________English，because he thinks it of no use.
A．to stop to practise reading
B．stopping practising reading
C．to stop practise reading
D．stopping to practise to read
成人主要的造血器官是
A．骨髓
B．肝
C．脾
D．淋巴结
E．胸腺
