— How much do you know about the 3D film technology?

— A little. Not until ________ the hot movie Avatar ________ some about it.

A．did I see; did I begin to learn

B．I saw; I began to learn

C．I saw; did I begin to learn

D．did I see; I began to learn

当市场处于牛市时，应选择B系数较小的股票。( )