on the front的意思是在…战线。例如：He was on the front lawn, measuring out two circles. 他在前面的草苹上丈量并标记出两个圆圈。on the front of的意思是在前的；靠前面的；在…的前面。例如：on the front of the house. Her father used to perch her on the front of his bike.