Trap Nouns in the Past: био, била, било

In the past tense, the participle of бити agrees with the subject in gender and number: био (masculine), била (feminine), било (neuter); in the plural били, биле, била. With trap nouns, go by the noun's real gender, not by its ending:

• Nouns for men are masculine, and so are ауто and такси: тата је био, деда је био, ауто је био.
• Feminine nouns take била, even without -а: ноћ је била, со је била, кћи је била.
• кола (car) exists only in the plural and is neuter: кола су била.
• наочаре, панталоне, новине exist only in the plural and are feminine: биле.
• Regular neuters take било: дете је било код баке (the child was at grandma's).

A plural-only noun takes су, even when it means one thing.