Classify each of the following as either a citrus fruit or non citrus-fruit: apples, pears, watermelons, lemons, clementines, mandarines

Apples are not a citrus fruit.
Pears are not a citrus fruit.
Watermelons are not a citrus fruit.
Lemons are a citrus fruit.
Clementines are a citrus fruit.
Mandarines are a citrus fruit.