评价预防接种群体效果的免疫学指标是（）。
A.抗体阳转率
B.保护率
C.效果指数
D.发病率
E.病死率
参考答案：A
He always did well at school _____ having to do part-time jobs every weekends. [ ]
A. in spite of
B. regardless of
C. on account of
D. in case of
禁止标志是禁止人们不安全行为的图形标志，其基本形式是（）。
A.正三角形边框
B.圆形边框
C.带斜杠的圆边框
D.正方形边框
