The bus (which goes to the airport){定語從句修飾先行詞the bus } runs every half hour .
The bus runs every half hour .是主句為什么我說 The bus which runs every half hour goes to the airport 說我錯呢你這句語法上沒錯。不過意思變成“第半小時一趟的公共汽車去機場‘第一句的意思是’去機場的公共汽車每半小時一趟‘