我国开始使用铁农具是 [ ]
A．商朝
B．西周时期
C．春秋时期
D．战国时期
答案：C
All possible means ___ been tried to stop the air______.
A．has, polluted
B．have, polluting
C．have, being polluted
D．has, being polluted
中国近代甘心为变法流血的第一人是谁？
