A．Body fluid from test animals may contain such biologically active metabolites． B．A positive control group, i.e a group of animals in which the effect of a drug known to be positive is examined． C．Disease models can be made by treating animals with certain chemicals or other modalities． D．For study of those herbal medicines, animal models may need to be established according to those principles． E．An examination Of literature may help to select the species and test systems． 找出相应的英文