Final answer:
The letters e, i, and y following the letter c make it produce the soft /s/ sound, as in the example of 'city'.
Step-by-step explanation:
The letters that signal the soft c sound, pronounced as /s/, are e, i, and y. When the letter c has one of these letters immediately following it, it is pronounced /s/. For instance, in the word 'city', the 'ci' is pronounced as /s/ because of the presence of 'i' immediately after 'c'.