【简答题】运动副可分为高副和低副,其中低副包括 和 。
【单选题】The major difficulty in developing space travel is that ______.
A.
there is no clear destination in space
B.
it is too risky and expensive for people to go beyond the orbit
C.
the current space propulsion systems can not meet the needs for the long space travel
D.
there is not enough energy for spacecraft to gain velocity
【单选题】下列基于ICMP的扫描请求,不遵循查询/回应方式的是
D.
destinationunreachable
【简答题】根据运动副两构件的 不同,运动副可分为高副和低副。
【简答题】D-异抗坏血酸钠的鉴别试验在无色火焰中燃烧,火焰即显 。