At midnight,Peter was awakened by heavy knocks onthe door.这句中knock为什么加s

At midnight,Peter was awakened by heavy knocks onthe door.这句中knock为什么加s
At midnight,Peter was awakened by heavy knocks on
the door.
这句中knock为什么加s

At midnight,Peter was awakened by heavy knocks onthe door.这句中knock为什么加s
heavy knocks on the door重重的敲门声
knock可以用复数
祝你学业进步!

knock=敲门声，是名词。加s表示多次敲门声。