火星是离太阳第四颗行星。

Mars is the fourth planet from the Sun.

地球是一颗行星，它绕着太阳转。

The earth is a planet and it goes around the sun.

另外七颗行星也绕着太阳转。

Seven other planets also go around the sun.

我们刚刚开始探索其他行星。

We have just started to explore other planets.

这个行星很大。

The planet is very big.