有关商品谷物农业的叙述，正确的是[ ]

A．主要分布在美国、加拿大、印度等

B．商品谷物农场都是家庭经营方式

C．我国东北和西北也有商品谷物农业

D．商品谷物农业主要包括水稻种植业

At first his plan seemed impossible to put into practice, but ___it turned out to be quite easy.

A. ever since      B. so far      C before long       D. above all