необходим

см. тж. совершенно необходим; требоваться

• Cobalt is required in small amounts by plants and animals.

• In science, as opposed to pure philosophy, observable facts are requisite.

• To attain the high performance, powerful turbojets, rockets, or ramjets became a necessity.

• It takes at least a minute for the chamber to come to equilibrium.

• New approaches are called for.