负数a与它的相反数的差的绝对值是 [ ]
A.2a
B.0
C.-2a
D.±2a
答案：C
Nineteenth-century scholars tried to trace the origins of modern languages to ancient Hebrew.
A．limit
B．connect
C．convert
D．draw
机车安全线的有效长度一般不会小于（）米。
A.30
B.40
C.50
D.60
