Suddenly,I hear Charlie barking loudly.中的barking为什么要加ing?

Suddenly,I hear Charlie barking loudly.中的barking为什么要加ing? bark是名词那barking 呢?we can hear betty"s dogs barking .为什么是 bar 同义句转换：The dog is barking loudly.The dog is barking ____ ____ Barking dogs seldom bite为什么不是barked? 1.I am frigtened of the barking dog、 "Barking dogs don’t a barking dog Barking dogs seldom bites barking dog seldom bite suddenly out of the house ran a dog,barking at them i seem to hear someone knocking at the door,knocking为什么要加ing 为什么i will go swiming 中的swiming要加ing,