Spelling the /k/ sound before a vowel: is it c or k?

If the vowel after the /k/ is a, o or u, we usually use c:

Examples:

call, carrot
copy, colour (US color)
cup, cucumber

If the vowel is e or i, we usually use k.

Examples:

keep, kettle
kilt, kitchen

If a c is followed by e or i then it makes the /s/ sound.

Examples:

certain
circle, cinema

If the next letter is a consonant e.g. r or l , we almost always use c.

crab, cricket, crumb
club, close, clap