There are four shi(是) sentences below in Chinese in brackets, and their translation as well. Which shi(是) is translated into “be”?（）

A.Purple belonged to the emperor because of its associations with the north star.

B.It is a closed residence with only one gate leading to the outside

C.The Forbidden City stands as the largest complex of palace buildings anywhere in the world

D.Hong Kong-Zhuhai-Macao Bridge, the world’s longest sea bridge, was opened on 23.

正确答案：B