辅币是( )
A.无限法偿货币 B.大额通货 C.有限法偿货币 D.贵金属铸造的货币
参考答案:C
While income worry is _______ rather common problem of the aged, loneliness is another problem that ________ aged parents may face.
A.a; 不填
B.the; 不填
C.a; the
D.the; the
超声波在弹性介质中的速度是()
A、质点振动的速度
B、声能的传播速度
C、波长和传播时间的乘积
D、以上都不是