is后面加什么时态

例句：

The clear inference is that the universe is expanding.

显然结论是宇宙在扩大。

It is essential that your diet is varied and balanced.

重要的是你的饮食应当是多样而平衡的。

Today is Tuesday, so tomorrow is Wednesday.

今天是星期二，那么明天就是星期三。

It is a mild morning and the sun is shining.

这是一个和煦的早晨，太阳在照耀着。