DIAO-4

('diao' in the fourth tone)

There are some 21 standard Chinese characters with a 'diao' pronunciation. In five of them, 周 is the sound-defining component, even though as a character spoken by itself, the sound of 周 is 'zhou', not 'diao'.

掉 = diao(4) = to fall down

Or:

掉下去 = diao(4) xia(4) qu(4) = to fall down (of things)

However, please note that 掉 is used only for things, not for people. The word for people falling down is:

摔 = shuai(1) = to fall down, to tumble

The more common two-character expression is:

摔倒 = shuai(1)dao(3) = to fall down

*****

调 = to investigate

The preferred two-character version is:

调查 = diao(4)cha(2) = to investigate

查 = cha(2) = to check