—Ten years ago.
A:when you taught in this school
B:when did you teach in this school
C:how long you taught in this school
D:how long did you teach in this school
读图(阴影部分为黑夜),回答下列各题。
小红利用一个焦距为10cm的凸透镜作放大镜去观察植物标本,则标本离凸透镜的距离应该是()