"ua" is a combination of "u" and "a." See Unit 1 for the pronunciation of "a" and Unit 2 for the pronunciation of "u."
The stress is on "a;" therefore, the tone mark should be placed on top of "a."
wā, wá, wǎ, wà
When "ua" is not following an initial, it is written as "wa."
"uai" is a combination of "u" and "ai." See Unit 3 for the pronunciation of "ai" The stress is on "a;" therefore, the tone mark should be placed on top of "a."
wāi, wái, wǎi, wài
When "uai" is not following an initial, it is written as "wai."
"ueng" is a combination of "u" and "eng." See Unit 5 for the pronunciation of "eng."
The stress is on "eng;" therefore, the tone mark should be placed on top of "e."
wēng, wéng, wěng, wèng
"ueng" is always written as "weng" since it never follows an initial.
