triennial

adj lasting for or happening every three years 持续三年的; 每三年一次的.

tribe, tribesman, tribulation, tribunal, tributary, tribute, trice, triceps, trick, trickery, trickily, trickiness, trickle, trickle charger, trickster, tricky, tricolour (US tricolor), tricycle, trident, tried, triennially, trier, trifle, trifler, trifling, trigger, trigger-happy, triglyceride, trigonometric, trigonometrical, trigonometrically, trigonometry, trike, trilateral, trilaterally, trilby, trilingual, trill, trillion, trillionth, trilobite,