Q20:

Construction of the Roman Colosseum, which was officially known as the Flavian Amphitheater, began in A.D. 69, during the reign of Vespasian, was completed a decade later, during the reign of Titus, who opened the Colosseum with a one-hundred-day cycle of religious pageants, gladiatorial games, and spectacles.

A.       which was officially known as the Flavian Amphitheater, began in A.D. 69, during the reign of Vespasian,

B.       officially known as the Flavian Amphitheater, begun in A.D. 69, during the reign of Vespasian, and

C.      which was officially known as the Flavian Amphitheater, began in A.D. 69, during the reign of Vespasian, and

D.      officially known as the Flavian Amphitheater and begun in A.D. 69, during the reign of Vespasian it

E.       officially known as the Flavian Amphitheater, which was begun in A.D. 69, during the reign of Vespasian, and

这个题B和C只差一个which was，怎么区分呢？ 答案是C。

谢谢高手，牛人指教！！