4 sentences

1. 彩虹是一种自然现象。

   cǎi​hóng shì yī zhǒng zì​rán xiàn​xiàng.

   A rainbow is a natural phenomenon.

   Source: Tatoeba

2. 酸雨不是自然现象。

   suān​yǔ bù shì zì​rán xiàn​xiàng.

   Acid rain is not a natural phenomenon.

   Source: Tatoeba

3. 这种自然现象非常罕见。

   zhè zhǒng zì​rán xiàn​xiàng fēi​cháng hǎn​jiàn.

   This natural phenomenon is very rare.

   Source: Dong Chinese Dictionary

4. 这种自然现象具有明显的周期性。

   zhè zhǒng zì​rán xiàn​xiàng jù​yǒu míng​xiǎn de zhōu​qī​xìng.

   This natural phenomenon exhibits clear periodicity.

   Source: Dong Chinese Dictionary