必备条件

kuàng yuán céng shì chéng kuàng zuò yòng de wù zhì jī chǔ hé bì bèi tiáo jiàn

矿源层是成矿作用的物质基础和必备条件。

Source bed is a material base and essential condition of mineralization.

jiào xué jīng yàn shì zhè xiàng gōng zuò de bì bèi tiáo jiàn

教学经验是这项工作的必备条件。

Previous teaching experience is a necessary qualification for this job.