The part - sun - is actually pronounced the same way in each of the examples you have given
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CalifJimThe n, for example, is pronounced differently when it is followed by a g or k or c or x or q, compared with when it is followed by other letters.Heh, now you are forcing me to ask you about some interesting stuff!
unsung, asunder.
Because english lack a one to one correspondence, this mean that it is not as in spanish that we have one letter one sound.
The reason is because english comes from differents languages