How often should the lubricating oil of a diesel engine be changed？A.After every tripB.Eve

How often to the dentist？A、you go toB、do youC、do you go

In a diesel engine lube oil system, which of the following parts should be lubricated firs

听力原文：How often do we need to change the oil in the car？ （A) Every 3 months or every 3,

How often should the man take the medicine？A．Three times a day with meals.B．Three times a

How often（)to the dentist？A. you go toB. do you goC. do you

According to the writer how often should parents