required

必需的

Being a substance that is required for normal functioning but does not need to be included in the diet because of the body's ability to synthesize it from other nutrients.

（氨基酸）非必需的是正常的运转所需要的物质的，但因为机体有从其它营养成分合成它的能力，因此不需要被包括在日常的食物中的

The ships required the protection of naval and air power.

船只本身需要海军和空军的保护。