Basic Guidelines For English Spellings
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1Forming plurals of nouns ending in sibilant sounds.
2Forming plurals of certain nouns ending in -o.
Variant of -s.
1Forming the third person singular of the present tense in verbs ending in sibilant sounds.
2Forming the third person singular of the present tense in verbs ending in -o (but not -oo)
Variant of -s.