题目

-Hi, Tracy,you look tired. --I am tired.I_____the living room all day. A. painted                       B. had painted C. have been painting              D. have painted 答案：C2．海水中氯元素的质量分数为1.82%，假设氯元素都是以氯化钠的形式存在，则海水中的氯化钠的百分含量为3.00%．