1.Whereas when we are asleep, they work very, very hard at removing all the waste that builds up when we are awake.
build up (交通)阻塞,(交通)越來越擁擠,(車輛)擁擠起來;(用磚等)堵塞(門、窗等):
During the summer holidays,traffic builds up along the roads to the coast.
每到暑假,在去海濱的路上車輛就擁擠起來 。
The doorway in the west side was built up by the neighbour's house.
西面的門口被鄰居的房子阻塞了 。