题目选项分析

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

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.