发病率
参考答案：
确定暴露于某种危险因素下的健康人，在某一特定时间内发生某种疾病的可能性就是发病率。
Sally asked _______. [ ]
A. how can she get to the zoo.
B. how she can get to the zoo.
C. how she could get to the zoo.
D. where was the zoo.
