Sentence:One caravan trail developed into the Silk Road. During the height of caravan travel, which lasted until the 19th century, a single [e1]caravan[/e1] of Muslim [e2]pilgrims[/e2] journeying from Cairo and Damascus to Mecca might employ as many as 10,000 camels.
 e1: caravan. 
 e2 : pilgrims.
Answer: Member-Collection(e2,e1)