OG12 SC-111

LuckyStars

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
不明白OG对D选项的解释，OG说 Roman Colosseum已经试最后一个动词即was completed的主语了，这是什么意思？was completed的主语难道不是construction吗？