∵a与1a，互为倒数，a=1a，
∴a=±1．
It is generally said that man’s desire is hard _______.
A．to satisfy
B．to be satisfied
C．to met
D．to being satisfied
使用带T字的移动减速信号牌进行防护时，动车列车的防护距离为（）m.
A.1000
B.1200
C.1400
D.1600
