写英文句子时，要有明确的中心点，包括主语的人称、数目以及谓语动词的时态、语态和情态等。如果句子的中心点随便改变或转移的话，句子结构可能陷入模糊状态，使人困惑，也削弱了文章气势。

下面就是些有关句子中心点转移的例子：

⒈随便转移主语和语态，如：

① Cocks were heard crowing as the hikers approached the farm.

在一个短短的复杂句里，原本的主句主语突然变成副词从句的主语“the hikers”，动词语态则以被动形式出现在另一个文句里。这样的转变没有好处，也没有必要。这句话可修改为：

The hikers heard cocks crowing as they approached the farm.

这里两个主语保持中心点，一气呵成，明确多了。

② The tourists stayed at a holiday hotel and much of their time was spent there.

这里的两个并列句的主语从“the tourists”转入“much”，动词则以主动语态变成被动语态;这样做，必要吗?还是改写一下好：

The tourists stayed at a holiday hotel and spent much of their time there.

⒉随便转移人称和数目，如：

③ Everyone will feel happy if you enjoy good life.

④ Kelvin enjoys cigarette smoking, but they make his throat sore.

在③里，人称“everyone”和“you”不协调所以要把“you”改成“he”或“everyone”变成“you”。如果“you”变成“he”，谓语动词“enjoy”要变成“enjoys”以便动词和主语一致：

Everyone will feel happy if he enjoys good life. You will feel happy if you enjoy good life.

在④里，用“they”指“cigarette-smoking”，不符合语法规则，必须把“they make”改为“it makes”人称和数目才配合。不这样改也行，但“they”就要和新主语“cigarettes”。(不是cigarette smoking)搭挡。

⒊随便转移动词时态和情态，如：

⑤ The robber considered himself unlucky, rushed to the door, and trying to escape.

这句子中三个动词的时态要一致，不可以让最后一个突然改变形式，因此“trying”要改为“tried”。

⑥ Hold your gun tightly, take aim, and you can shoot.

这里的三个短句中，两个是祈使句，为什么最后一个突然变成陈述句?非改不可：

Hold your gun tightly, take aim and shoot.

You can hold your gun, take aim and shoot.

⑦ As I have made everything clear to him, I expected that he will let bygones be bygones.

显然的，这里的三个动词的时态都可以是现在式，因此主句中的“expected”要改为“expect”才行。