题干
I'm very proud that Beijing is one of _______ cities in the world.
A：big
B：bigger
C：biggest
D：the biggest
答案(点此获取答案解析）
D
I'm very proud that Beijing is one of _______ cities in the world.
A：big
B：bigger
C：biggest
D：the biggest
,则三棱锥P-ABC的侧面积的最大值为