And this is connected by a thread-this must be seen clearly.

There is no answer to this question by exclusion.

If rooms 9 and 9 are excluded, birdie 8 must be used, and birdie 1 should be added. Otherwise, birdie 8 cannot be used in rooms 8, 7 or even 6, and it can only be removed, so it is not enough.

By analogy, there can be no answer to this question.