"ia" is a combination of "i" and "a." See unit 1 for the pronunciation of "i" and "u." When "ia" is pronounced, the stress is on "a", not "i". The tone marks is placed on top of "a."
yā, yá, yǎ, yà
When "ia" is not following an initial, it is written as "ya."
When "an" in "ian" is pronounced, its pronunciation is slightly different from when it is pronounced as a stand-alone sound. Therefore, "ian" is not entirely a combination of "i" and "an."
"an" in "ian" is pronounced with the position of the tongue slightly lower than when "an" is pronounced as a stand-alone sound.
"an" in "ian" is similar to "end" without "d" in English. In "ian," the stress is on "an," not "i." The tone marks is placed on top of "a".
yān, yán, yǎn, yàn
When "ian" is not following an initial, it is written as "yan."
"ü" is sometimes referred to as an umlaut.
When "ü" is not following an initial, it is written as "yu." The diacritic (the two dots on top of u) should not be used.
However, "ü" or "yu" should not be pronounced by starting with "i" and following it with “u;” instead, the lips should be rounded as if to pronounce "u," but the tongue is position to pronounce "i".
yū, yú, yǔ, yù
When "ü" is following "j," "q," or "x," the diacritic (the two dots on top of u) should not be used since it is not possible for "u" to follow "j," "q," or "x." jū, jú, jǔ, jù
