not only but also连接的句子时态必须一致吗?

不一定.但是,主从句要同为现在,同为过去.
Not only is the teacher himself interested in football,but all his students are also
beginning to show an interest in it.
一个是一般现在时,一个是现在进行时.
下面这种情况,连接的不是完整句子,它们时态要一致.
It not only keeps me fit but also helps me concentrate on my soul.
它不仅使我保持健康,而且也帮助我集中精神.