They played a joke on him by letting down the tyres of his bike.他们捉弄他，把他的自行车的轮胎放了气。The aircraft is letting down to land.飞机正向地面下降。Any boy who misbehaves will be letting down the whole school.任何行为不端的孩子都会让整个学校蒙羞。The irate colonel blared at the troops for letting down the regiment.怒气冲冲的上校向士兵们吼叫，因为他们给全团丢了脸。