4 sentences

1. 这种胶水粘得不固，东西很容易掉。

   zhè zhǒng jiāo​shuǐ zhān de bù gù, dōng​xi hěn róng​yì diào.

   This glue doesn't hold firmly; things fall off easily.

   Source: Dong Chinese Dictionary

2. 这个化学反应涉及到气、液、固三相的转化。

   zhè​gè huà​xué fǎn​yìng shè​jí dào qì, yè, gù sān xiàng de zhuǎn​huà.

   This chemical reaction involves the transformation of gas, liquid, and solid phases.

   Source: Dong Chinese Dictionary

3. 固所愿也，不敢请耳。

   gù suǒ yuàn yě, bù gǎn qǐng ěr.

   It is exactly what I have always desired, but I did not dare to ask.

   Source: Dong Chinese Dictionary

4. 学外语固非易事，但很有趣。

   xué wài​yǔ gù fēi yì​shì, dàn hěn yǒu​qù.

   Learning a foreign language is certainly no easy task, but it is very interesting.

   Source: Dong Chinese Dictionary