【题目】Experts warn that medical waste from hospitals, if properly, may contribute to spreading diseases.
A. not handled
B. not being handled
C. not to be handled
D. not having been handled
在线课程【答案】A
【解析】句意：专家警告说，如果医院的医疗垃圾不能正确的处理，可能会导致疾病的蔓延。If 引导的条件句的主语是 medical waste from hospitals ，与handle之间是被动关系，故选A项。