已知等腰三角形的一边长为3cm,且它的周长为12cm,则它的底边长为( )
A:3cm
B:6cm
C:9cm
D:3cm或6cm
There is a common belief among the students in our school ______ they should try their best to learn and reach the peak of their academic performances.
观察图片。回答下列问题
某女同学手里提着一个重力为10N的皮包沿水平方向前进了10m,则该同学对皮包做的功为____J.
①出现了最早的纸币
②发明了活字印刷术
③开创了科举考试制度
④形成了词创作的繁荣局面