3 sentences

1. 改革开放是决定当代中国命运的关键抉择。

   gǎi​gé​kāi​fàng shì jué​dìng dāng​dài Zhōng​guó mìng​yùn de guān​jiàn jué​zé.

   Reform and opening up is a crucial choice that determines the fate of contemporary China.

   Source: Dong Chinese Dictionary

2. 在那个时代，无数年轻人投身于改革开放的大潮中。

   zài nà gè shí​dài, wú​shù nián​qīng​rén tóu​shēn yú gǎi​gé​kāi​fàng de dà​cháo zhōng.

   In that era, countless young people threw themselves into the tide of reform and opening up.

   Source: Dong Chinese Dictionary

3. 改革开放四十年来，中国的面貌发生了天翻地覆的变化。

   gǎi​gé​kāi​fàng sì​shí nián lái, Zhōng​guó de miàn​mào fā​shēng le tiān​fān​dì​fù de biàn​huà.

   Over the past forty years of reform and opening up, China has undergone earth-shaking changes.

   Source: Dong Chinese Dictionary