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