A:9和10
B:14和25
C:25和21
D:7和84
小刚上小学时是个学习成绩很好的学生,可进入初中以后,成绩有很大的滑坡,他父母和他都非常着急。作为小刚的同学,你如何劝他呢?在下列的选项中,你认为哪种观点是错误的( )
J____ from his face on which there was a confident smile, we know that he didn't lose heart.
两个同心圆的半径之比为3:5,AB是大圆的直径,大圆的弦BC与小圆相切,若AC=12,那么BC=( )