[单选题]
Which of the following is/are true t(jeq ,xj:a2s4c yvh ajo:7, tfor holozqrbawu 5a+7y :;m+pwh oic nutrition?
I. Demonstrated by saprotrophs
II. Involves complete or partial ingestion
III. Food is digested internally
A. I and II only
B. II and III only
C. I and III only
D. I, II and III