题目

When Colonel Harland Sanders retired at the age of 65, he had little to show for himself, except an old Caddie roadster, a $105 monthly pension check ,and a recipe for chicken. Knowing he couldn’t live on his pension, he took his chicken recipe in hand, got behind the wheel of his van (货车),and set out to make his fortune. His first plan was to sell his chicken recipe to restaurant  owners, who would in turn give him a residual (酬金)for every piece of chicken they sold—5 cents per chicken. The first restaurateur he called on turned him down.  So did the second.  So did the third. 将一物体放在凸透镜前，在距离凸透镜26cm的光屏上得到放大的像，则该凸透镜的焦距可能是（　　）A．10cmB．20cmC．30cmD．40cm