Aware of the harsh facts concerning the dangers to the environment, scientists in various countries have sounded a serious warning to mankind.
本题考查常见名词短语的使用。
意识到···：be aware of···；严峻事实：the harsh fact；严重的警告：a serious warning。
句子结构：主干：科学家向人类发出了警告；“意识到威胁人类生存环境的那些严峻事实”为伴随状语。
