【单选题】The price of public transportation in Beijing has doubled twice since 1989, but it is still a bargain. Using the subway and minibuses used to show class status now people of all classes take them, whi...
【简答题】Since all roads are not
perfectly smooth, and the transmission is fixed, the drive shaft has to be
flexible to absorb the shocks of bumps in the road. Universal, or “U-joints”
allow the drive shaft to...