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.

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

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

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

the answer is C,but B seems reasonable

B的begun不好，过去分词做修饰的话，and之前只有主语，没有谓语动词了

Construction of the Roman Colosseum，【officially known as the Flavian

Amphitheater】修饰【Roman Colosseum, begun in A.D. 69】过去分词修饰

Construction, 【during the reign of Vespasian】状语,and+谓语

这个结构里，and之前没有谓语动词，只有主语

Cbegan是过去式，作为动词

结构 Construction of the Roman Colosseum。。began。。and was  completed 。。。

大家有没有想这题中同谓语和which从句的区别？

我的理解是，which这里指代the Roman Colosseum，根据which的指代原则（就近和逻辑意思）很清楚。

而B中同谓语officially known as the Flavian Amphitheater只能修饰逗号前主语construction,错

open to discuss