Considering the severe fact of global warming, the top _______ of all nations is to reduce CO2 emissions and increase use of renewable energy.  [ ]

A. priority

B. impact

C. issue

D. event

自行车链条刚与柔的结合体现了分离原理的（）。

A.空间分离

B.时间分离

C.条件分离

D.整体与局部的分离