–– Beijing is a big city, isn't it?
–– Yes. In fact, it's one of ________ cities in the world.
A:big
B:bigger
C:biggest
D:the biggest
新电灯泡的玻璃上常有一点暗红物质以除去灯泡内残留的氧,该物质是( )
在△ABC中, AD→ =2 DC→ , BA→ = a→ , BD→ = b→ , BC→ = c→ ,则下列等式成立的是( )