You must look right before you cross the road in Hong Kong.这一句cross是从句谓语；
2.We must look right before crossing the road.而这一句crossing是before+v-ing形式， 也就是(介词+v-ing); 也可以理解为（连词+v-ing：表主动）
You must look right before you cross the road in Hong Kong.这一句cross是从句谓语；
2.We must look right before crossing the road.而这一句crossing是before+v-ing形式， 也就是(介词+v-ing); 也可以理解为（连词+v-ing：表主动）
