Most tower clocks are still kept in Europe.Some of them have been 400 or 500 years old.
1.Most tower clocks are still kept in Europe.这句中为什么are是一般现在时,但后面的kept却是过去式?
2.Some of them have been 400 or 500 years old.这句中为什么have是一般现在时,但其后的been 是过去式?可否将这句改为--Some of them have 400 or 500 years old.