Question

give the plural of these nouns univercity  sky    party      way        leafthief          ski      key        tragedy  comedy day            taxi    story      language    knife

Answer 1

university — universities,
sky — skies,
party — parties,
way — ways,
leaf — leaves,
thief — thieves,
ski — skis,
key — keys,
tragedy — tragedies,
comedy — comedies,
day — days,
taxi — taxis (или taxies),
story — stories,
language — languages,
knife — knives. 

Answer 2

universities  skies    parties      ways        leafthieves          skis      keys        tragedies  comedies days            taxis    stories      languages    knives