乃是的英语怎么说

乃是的英文：
to be

The very reputation of being strong-willed, plucky, and indefatigable is of priceless value. ——Charles Robert Darwin
意志坚强、胆量过人和不屈不挠的名声，乃是一种无价之宝。——达尔文

Perhaps the most thoroughly analyzed hereditary disease are those in which abnormal hemoglobin molecules are produced
也许最详尽分析过的遗传性的疾病，乃是那些产生异常血红蛋白的遗传病。

Variety is the spice of life.
变化乃是生活的情趣。

Temperance is the best physic
克制乃是最好的治疗

This custom is a relic of ancient times.
这习俗乃是古代遗风。

Venice is the child of her own tumultuous past.
威尼斯乃是它自己的动乱岁月的产物。

This special property of laser light is the basis of holography
激光的这种特殊性质乃是全息照相的基础。

Venice is the child of her own tumultuous past
威尼斯乃是它自己的动乱岁月的产物。

Truth's best ornament is nakedness.
不加掩饰乃是真理的最好装饰。

Another fundamental concept in ecology is that energy flow through the ecosystem
生态学的另一个基本概念乃是生态系统中的能流。