The standardization of futures contracts promotes liquidity because:()

A. all the participants in the market know exactly what is being offered for sale, and they know the terms of the transactions. 

B. it guarantees that all of the traders in the futures market will honor their obligations and that futures contracts trade in a smoothly functioning market. 

C. it provides a safeguard whereby traders are required to realize any losses in cash on the day they occur.

（）（）（）的变化，是电视摄像中视点变化的基本要素。