Tổng diện tích tất cả các mặt của tứ diện đều cạnh $a$ bằng
![](https://m.moon.vn/Images/Teachers/nguyenoanh8892/To%C3%A1n/04/1/2.png)
A.
![](https://m.moon.vn/Images/Teachers/nguyenoanh8892/To%C3%A1n/04/1/2a.png)
B.
![](https://m.moon.vn/Images/Teachers/nguyenoanh8892/To%C3%A1n/04/1/2b.png)
C.
![](https://m.moon.vn/Images/Teachers/nguyenoanh8892/To%C3%A1n/04/1/2c.png)
D.
![](https://m.moon.vn/Images/Teachers/nguyenoanh8892/To%C3%A1n/04/1/2d.png)
Đáp án D
![](https://m.moon.vn/Images/Teachers/nguyenoanh8892/To%C3%A1n/04/1/2e.png)