经济发展是国家的核心部分。

Jīngjì fāzhǎn shì guójiā de héxīn bùfen.

Economic development is a core part of the country.

了解客户需求是销售工作的核心。

liǎojiě kèhù xūqiú shì xiāoshòu gōngzuò de héxīn.

Understanding customer needs is the core of sales work.

这个问题的核心是什么？

zhège wèntí de hécōng shì shénme?

What is the core of this problem?