1. What causes certain tones (bù, bú) to change? They change depending on the preceeding tone.
They change depending on the tone following bu.
They change depending on regional accents.
They change when their meanings change.

2. What different meanings does the dual-pronounced character xíng, háng 行 have?
can do something, sleep
ability to do something, unable to do something
able to do something, a trade (also bank)
professions, careers

3. Which of the following tone's for 一 yī is correct?
yìzhī
yīzhī
yizhī
yǐzhī