As the ozone layer in the Earth's upper atmosphere thins, it allows more ultra-
; w# N( Z: R# M" X2 Jviolet radiation from space to pass through the upper atmosphere. Thus, since # g0 _# m; A8 U& q) A9 f C& q. A! L
the ozone layer recently started to thin over North America, the upcoming mea-2 ], E* C. a( x7 [/ Z8 j! M: T/ z% O
surement of ultraviolet radiation over North America should show that ultraviolet
0 d* {/ F ?) n3 J5 ~radiation has increased in intensity at ground level there.
2 D" Y, @& a! b$ R* E7 G6 n Which of the following, if true, most seriously weakens the argument given?
Y! `; s% K$ C The ozone layer in the Earth's upper atmosphere has thinned to a much
7 }' |+ B4 o, _ t. O greater extent over the Earth's southern pole than it has over North
8 b4 L4 w$ \: f# R0 Z9 t0 j* m America.
/ I s$ ~* W9 H/ \" H% x During the next decade, the countries of North America will completely halt
2 _. R5 z9 a, _& n) l production of the chemicals that cause the ozone layer to thin.
7 N$ g: O3 F- N/ `/ H* ~ Clouds absorb ultraviolet radiation, and cloud cover has been increasing 0 B& d; A7 d0 R5 c4 ]" C) {$ m8 |
over North America in recent years because of changing weather patterns. , h9 G$ z* X. a& v# p
The instruments that are used to measure ultraviolet radiation near the Earth's
& M' s9 C8 C9 g surface have not become significantly more accurate in recent years. 4 T$ b" `7 ~# }( M- n- j+ r' z
At any given time, ultraviolet radiation is typically more intense on mountain -
+ W" M7 I7 }; b) `( N. O0 l tops than at low-lying plains. |