为了增加汽车轮胎的耐磨性，常在轮胎的橡胶加入的耐磨物质是 [ ]

A、石墨粉       

B、活性炭        

C、炭黑         

D、木炭粉

Here are the photos _______ in Beijing.

A．who are taken

B．that took

C．which I was taken

D．that were taken