选项ABCD都为Grade1类的子类，能正确输出‘we have 20 students’的选项是（）(选择两项)

//climg.mukewang.com/598bf9b3000180c904360157.jpg

 

 

A

//climg.mukewang.com/598bf9cc0001443003960159.jpg

 

 
B

 

//climg.mukewang.com/598bf9f300018b3503610188.jpg

C

 

//climg.mukewang.com/598bfa070001b75f03230165.jpg

D

 

//climg.mukewang.com/598bf9e0000122f703620213.jpg

 

CD