农田弃耕后的演替，按演替发生的时间为( )
A．世纪演替 B．长期演替C．快速演替 D．以上三者都不是
参考答案：C
______up the recovery process, the government declared a public health emergency in the Gulf Coast areas hit by the hurricane.
A．To speed
B．Speeding
C．Speed
D．Having sped
洛氏硬度HRC测量时，采用（）压头。
A、金刚石圆锥
B、淬火钢球
C、淬火圆锥
