题干
I called you, but nobody answered. Where ____ you?
A：is
B：are
C：was
D：were
答案(点此获取答案解析）
D
I called you, but nobody answered. Where ____ you?
A：is
B：are
C：was
D：were
心，其收缩不能维持；用含有少量钙和钾的生理盐水灌注时，蛙心可持续跳动数小时。实验说明钙盐和钾盐 （ ）
