• In English the letter c is usually pronounced as a /k/ sound.
• We can also pronounce c as an /s/ sound.
• When c comes directly before the letters e, i or y we use the /s/ sound.
• In other cases we use a /k/ sound.
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Some words with both sounds:
bicycle
cycle
cybernetics
Exceptions:
soccer (we pronounce both the letters c as a single /k/ sound)
muscle.