The atmosphere again acts __1__ our protective blanket on __2__ .
Light gets through, and this is essential __3__ plants to make the food which we __4__ .
Heat, __5__ , makes our environments tolerable and some ultraviolet rays(紫外线的) penetrate the __6__ .
Cosmic(宇宙的) rays of v 英语四级完形填空模拟题十七(附答案详解) 标签：
