西周末年,昏庸的幽王上演了一场“烽火戏诸侯”的闹剧。诸侯率兵前往护卫周王是遵守了( )
A:封建制的法规
B:禅让制的规则
C:世袭制的传统
D:分封制的义务
点P(2,-5)关于原点的对称点Q的坐标为____.
China began to open to the outside world in the late 1970s. _________, there have been great changes in the country.
一入射光线与法线的夹角为60°,则反射角为____ ;若入射角增大10°,则反射光线与入射光线的夹角为____ 。