试题题干
Translate the following sentence into Chinese.
If the sky appears blue to us on earth, it is because the earth's atmosphere absorbs a certain number of blue rays of sunlight.
参考答案
试题解析
考点：the earth's atmosphere地球大气层；absorb吸收； a certain number of一定数量的。
句子结构：If 引导条件状语从句，主句为it is···，because引导表语从句。