单选题At ground level, nitrous oxides are bad enough, but when up high, atmospherically they bond with free ions to create dangerous smog particles.A but when up high, atmospherically theyB however, it is in the upper atmosphere in which it mayC but in the u
题目
单选题
At ground level, nitrous oxides are bad enough, but when up high, atmospherically they bond with free ions to create dangerous smog particles.
A
but when up high, atmospherically they
B
however, it is in the upper atmosphere in which it may
C
but in the upper atmosphere, they
D
however, but once in the upper atmosphere it is known to
E
as in the upper atmosphere they