下列三个句子中包含什么从句呢? p.p1%20%7Bmargin%3A%200.0px%200.0px%200.0px%200.0px%3B%20line-height%3A%2019.0px%3B%20font%3A%2013.0px%20%26%2339%3BHelvetica%20Neue%26%2339%3B%3B%20color%3A%20%23000000%7D ...the Mogao Caves, which were a key stop along the Silk Road... As one researcher who is working on the project explains... ...at the time when people travelled the Silk Road.