【温故知新】 阅读并使用关系词或括号内动词的适当形式完成下列句子，并体会其用法。 ①The power of the Yangtze River, ______ is the world’s third longest river, has been harnessed by the Three Gorges Dam. ②The Three Gorges Dam, ______ is the biggest construction project in China since the building of the Great Wall and the Grand Canal, has been built to control flooding and provide hydro-electric power for the central region of China.

which

which