AIR CONSISTS OF A COMBINATION OF NITROGEN AND OXYGEN …………. IN PLA...

ĐỀ THI OLYMPIC ĐỒNG BẰNG SÔNG CỮU LONG TRƯỜNG THPT THỊ XÃ SA ĐÉC

4. Air consists of a combination of nitrogen and oxygen …………. in place by gravity. A. are holding B. being hold C. holding D. held