TÌM 1 (X 2) X 2 C1 (X 2) C21 X 2 C22 21 (X 2) C23  2  3   3  ...

Câu 20: Tìm

1 (x 2) x 2 C

1 (x 2) C

2

1 x 2 C

2

2

2

3





2





3



 

3

 

B.

C.

D.

A.

1

2

3

4

5

6

7

8

9

10

D

D

A

C

B

A

C

A

D

B

11

12

13

14

15

16

17

18

19

20

A

A

A

C

C

D

B

XXX

A

C