__high levels of radiation can lead to serious health breakdown.A.exposing to B.being exposed toC.Exposed to为什么不能选C 不是being done 不能放在句首么

__high levels of radiation can lead to serious health breakdown.A.exposing to B.being exposed toC.to expose to D.exposed to __high levels of radiation can lead to serious health breakdown.A.exposing to B.being exposed toC.Exposed to为什么不能选C 不是being done 不能放在句首么 levels rad level qualificaitons为何改为levels of qualifications 求翻译Alltheexamshave different levels of difficulty human health levels of concern (LOC)如何翻译? 英语翻译后面的几个单词：levels of happiness. lower levels of为什麽 level后加s 翻译increased noise levels lead to a lack of concentration a couple of different levels 怎么翻译恰当 “a series of levels”是什么意思?就是这句话：The aquarium is built in a series of levels. 求翻译：Perceived levels of importance of various genres of metrics RAD什么是rad? 英语化学题,what is the maximum number of electrons ineach of the first four energy levels? Evaluation and Comparison of the Development of China's ‘Informationization’ Levels应该怎么译? 翻译There are many different levels of care providers within the area of nursing some keep a record of levels of pollution背景是保护海洋的方法