Loulan is believed by sandstorms from AD 200 to AD 400.
A. to be gradually covered over
B. to have been gradually covered over
C. being gradually covered over
D. having been gradually covered over
网友回答
A. to be gradually covered over
(答案→)B. to have been gradually covered over
C. being gradually covered over
D. having been gradually covered over
解析：考查be believed 结构的使用。 Sb be believed to do sth某人被认为做某事 sb be believed o have done sth 某人被认为做了某事
本句句意为罗兰被认为是在公元200年到公元400年之间被沙尘暴逐渐覆盖住了。