To make spanish nouns plural, you usually add to words ending in a

-as, consonant

-es, vowel

-es, consonant

-s, vowel

I believe the correct answer is C - es, consonant

Where are the sentences?

Agame in which two or four players strike a ball with rackets over a net stretched across a court. the usual form (originally called  lawn tennis  ) is played with a felt-covered hollow rubber ball on a grass, clay, or artificial surface.