4 sentences

1. 想起往事，他的心头泛起一丝苦涩。

   xiǎng​qǐ wǎng​shì, tā de xīn​tóu fàn​qǐ yī sī kǔ​sè.

   Thinking of the past, a touch of bitterness arose in his heart.

   Source: Dong Chinese Dictionary

2. 这种未成熟的果实吃起来非常苦涩。

   zhè zhǒng wèi chéng​shú de guǒ​shí chī qi​lai fēi​cháng kǔ​sè.

   This unripe fruit tastes very bitter.

   Source: Dong Chinese Dictionary

3. 提到那段失败的恋情，他露出了苦涩的微笑。

   tí​dào nà duàn shī​bài de liàn​qíng, tā lù​chū le kǔ​sè de wēi​xiào.

   Mentioning that failed relationship, he gave a bitter smile.

   Source: Dong Chinese Dictionary

4. 这种青橄榄嚼起来虽然有些苦涩，但回味很甘甜。

   zhè zhǒng qīng gǎn​lǎn jiáo qi​lai suī​rán yǒu​xiē kǔ​sè, dàn huí​wèi hěn gān​tián.

   Although these green olives are a bit bitter to chew, they leave a sweet aftertaste.

   Source: Dong Chinese Dictionary