Opera-dancer Viewed 2 times

Opera-glass Viewed 5 times

Opera-hat Viewed 1 times

Opera-house Viewed 4 times

Opera-singer Viewed 2 times

Operand (1) Viewed 18 times

Operand (2) Viewed 13 times

Operand (3) Viewed 22 times

Operant Viewed 2 times

Operant conditioning Viewed 6 times