有点击危险环境中使用的手持照明灯和局部照明灯应采用（）安全电压。A、24V B、36

( )规定了在未来某一特定时间、以某一特定价格买卖某一特定种类、数量、质量原生资产的权利。

A．期货合约

B．远期合约

C．期权合约

D．掉期合约

(66) is a one-way function that takes an arbitrarily long piece of plaintext and from it computes a fixed-length bit string. (67) is a protocol that most USENET machines how use it to allow news articles to propagate from one machine to another over a reliable connection. (68) is an approach preferred by cable TV providers. In this solution the fiber terminates at an optoelectrical converter and the final segment is a shared coaxial cable. (69) is a device used to connect two separate network that use different communication protocol. (70) js a digital-to-digital polar encoding method in which the signal level is always either positive or negative.

A．NNI

B．NRZ

C．NAK

D．NVT

合金性能的描述，正确的是（）

A.合金的凝点低于熔点

B.合金的延展性较所组成的金属高

C.合金的硬度较所组成的金属高

D.合金的导电性较所组成的金属好

E.合金的韧性较所组成的金属低

何谓残余应力？它会引起哪些后果？

胎儿心动过缓

A．胎儿心率每分钟持续在150次以上
B．胎儿心率每分钟持续在120次，历时10分钟
C．胎儿心率有基线摆动
D．胎儿心率静止型
E．胎儿心率有变异