The word "imperative" in the first paragraph most probably can be replaced by_________.

A．people' s growing interest in natural foods
B．natural food and health diet
C．the importance of fibre in foods
D．harmful effects of sugar

A．has been nourished by fertilizers
B．contains vegetable matter that has not been consumed
C．has had chemicals and fertilizer added to it
D．contains large quantifies of vitamins