"r" is one of the retroflex sounds. (The other three are "zh," "ch," and "sh" introduced in Unit 7.)
It is pronounced with the tip of the tongue curled (or raised) close to (but not touching) the roof of the mouth; therefore, "r" is similar to "sh."
The difference between "r" and "sh" is "r" is voiced, whereas "sh" is voiceless. This means that when "r" is pronounced, the vocal cords are vibrated.
"r" in Chinese can be considered similar to "r" in English. The major difference is that "r" in Chinese is not a lip-rounding sound.
The corners of the mouth should be pulled back except when "r" is followed by finals such as "u," "uo," "ui," "uan," "un," and "ong."
When "r" is followed by "i" (in spelling), the "i" is not pronounced as a regular "i," but is only used to bring the quality of a vowel to "r." See Unit 7 about "zhi," "chi," and "shi."
rī, rí, rǐ, rì
"iang" is a combination of "i" and "ang." See Unit 1 for the pronunciation of "i" and Unit 2 for "ang."
yāng, yáng, yǎng, yàng
The stress in "iang" is on "ang;" therefore, the tone mark should be placed on top of "a."
When "iang" is not following an initial, it is written as "yang."
"an" in the compound final "üan" is pronounced in the same way as it is pronounced in "ian." See Unit 6 for the pronunciation of "ian." "an" in "üan" is pronounced with the position of the tongue slightly lower than when "an" is pronounced as a stand-alone sound.
yuān, yuán, yuǎn, yuàn
The stress in "üan" is on "an;" therefore, the tone mark should be placed on top of "a."
When "üan" is not following an initial, it is written as "yuan." The diacritic (the two dots on top of "u") should not be used.
"üen" in Chinese is the combination of "ü" and "en." See Unit 1 for the pronunciation of "en."
When "üen" is following an initial, (which must be "j," "q," or "x,") the spelling is reduced to "un." But this should not affect the way "üen" is pronounced. The lips should first be rounded (puckered up) to pronounce "ü," and then become somewhat flat to pronounce "en." This means there is a slight change in the shape of the lips.
yūn, yún, yǔn, yùn; jūn, jún, jǔn, jùn
Whether "üen" is following an initial or not, the diacritic (the two dots on top of "u") should not be used, and the "e" in "en" is always omitted.
