What is plural noun?

If a noun ends in ‘s’, ‘sh’ or ‘ch’, then add ____?

If a noun ends in a consonant followed by ‘y’, then change the ‘y’ to ‘i’ and add ‘es’: artery – _{_________________.}

For all other regular nouns, add ‘___’

How ‘gh’ is pronounced differently in different words such as straight and rough?