FX系列PLC中LDP,表示什么指令()
A.下降沿
B.上升沿
C.输入有效
D.输出有效
参考答案:B
已知双曲线kx2-y2=1的一条渐近线与直线2x+y+1=0垂直,那么双曲线的离心率为______.
Questions 1-4
When was the Endangered Species Act passed?()
A.In the f9th century.
B.In 1973.
C.In 1998.
D.In the 21st century.