Definition: completely necessary Level: C2
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.
