During the past 120 years, the world        three waves of global economic integration（联合）.

A．witnessed

B．witnesses

C．has witnessed

D．will witness

任何一种天然的烹饪原料都不可能提供人体所需的所有营养物质，只有由多种食物互相搭配，这样的膳食才可能达到全面营养。