题目选项分析

Covering 71 percent of Earth's surface, the oceans play an essential role in maintaining the conditions for human existence on land, moderating temperature by the absorption of heat and carbon dioxide, and giving pure water back to the atmosphere through evaporation.

The oceans cover 71 percent of Earth's surface, play an essential role in maintaining the conditions for human existence on land, and moderate temperature by the absorption of heat and carbon dioxide, and giving pure water back to the atmosphere through evaporation.