大学英语：一个句子中的多个动词如果表示同时或几乎同时发生的动作或状态，其时态应保持一致。

Whenever the alarm clock rings in the morning,I yawn,stretch,and roll over for another five minutes of sleep.(一般现在时)

The following Tuesday I raced home from school,put the bag over my shoulder,dumped the magazines in and embarked on the highway of journalism.(过去时)

On the one hand,the government will do what it can to hunt for the hackers(黑客)and ,on the other hand,internet users will have to learn how to protect themselves.(将来时)

38.在并列句中，如两个或两个以上的动词所表示的动作不是同时或几乎同时发生（或不是同时期的状态）动词的时态按照动作发生的具体情况而定。

In the past,most families in China didn’t have a TV set,but now,a lot of them have not only TV sets,but also computers.(一般过去时和一般现在时)

He broke his leg in the accident,and according to the doctors,he will never be able to walk again.(过去时和将来时)