Undecided questions
tone changes: bu4 tai4 da4 bu4 tai4 xiao3

we change into:bu2 tai4 da4 bu2 tai4 xiao3.

:) i know that ~!

usually "bu" is the 4 sound.
BUT if the sound "bu" before the 4 sound(like bú tài dà), it turns to the 2 sound~

ep:

bu4 zhi1 dao4
bu4 neng2
bu4 ke3 yi3

bu2 shi4
bu2 yuan4 yi4
bu2 hui4
bu2 ai4


..................

Only bu4 changes to bu2. The rest keep their tones.

the simpest rule to remember is .

how do we know when to use 不bu4 or bu2 is that.

after the following word is the stress tone or (the fourth tone as “不” bu4） so it has to shift to the seconde tone (bu4>>>>bu2)

but likewise the following words is not the (fourth tone) it still remain the same as (bu4)

bu4+ fourth tone >>>>>bu2 + fourth tone
bu4 + 1,2,3 tones >>>>remain the same.

————————this is a must to remember!

good luck mi amigo

The answer is:
Bú taìdà bú tàixǎo
The rule to change the tone of "不(bu)" is:
1st bùgāo not tall
"不bu" + 2nd change to 4th bùxíng not ok
3rd bùhǎo not good

"不bu" + 4th change to 2th búqù don't go

不太大不太小。
bu2 tai4 da4 bu2 tai4 xiao3