求助GWD-17-Q21

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

B的begun不对，看句子意思可以知道说的是从AD69开始做，一个世纪后完工。began 和completed应该平行