z
Sounds kind of like "ds" in "bids", but voiceless.
zìjǐ
oneself
自己
zàijiàn
goodbye
再见
c
Sounds kind of like "ts" in "cats".
cí
word
词
cèsuǒ
bathroom
厕所
s
Sounds like "s" in "sick".
sì
four
四
sān
three
三
Single-syllable audio courtesy of the AllSet Learning Chinese Pronunciation Wiki, used with permission.
HSK word audio courtesy of Audio-cmn. (CC BY-SA 3.0)