13, 29, 15, 26, 17, 23, 19, … choose which pair of numbers comes next?

The correct answer is $\boxed{\text{A. }21, 23}$.

In this sequence, each number is 4 less than the number two places before it. So, the next number in the sequence is 4 less than 23, which is $\boxed{21}$.

Here is a table showing the sequence:

Number | 13 | 29 | 15 | 26 | 17 | 23 | 19 | 21 | 23
—–|——|——|——|——|——|——|——|—–
Difference | -4 | 4 | -4 | 4 | -4 | 4 | -4 | 4

Option B is incorrect because 20 is not 4 less than 21.

Option C is incorrect because 20 is not 4 less than 17.

Option D is incorrect because 25 is not 4 less than 23.

Option E is incorrect because 22 is not 4 less than 20.