一部可靠的智能手机是日常交流的必备工具。

A reliable smartphone is an ___indispensable tool for daily communication.

由于她的专业知识，她很快就对团队变得不可或缺。

She quickly became ___indispensable to the team due to her expertise.

清洁的水对人类生存是必不可少的。

Clean water is ___indispensable for human survival.