exit ramp的用法和样例：
例句
- A highway interchange at which two highways, one crossing over the other, have a series of entrance and exit ramps resembling the outline of a four-leaf clover and enabling vehicles to proceed in either direction on either highway.
苜蓿叶式立体交叉的公路两条高速公路的立体交叉道，一条穿过另一条，有一系列入口和出口坡道，与四叶苜蓿的外形相似，车辆在两条高速公路上均可驶入任一的两个方向
