乃是的用法和樣例：
例句
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因此，對一個從事社會活動的人來講，培養一種嗜好和新的情趣方式，乃是至關重要的對策。
The cultivation of a hobby and new forms of interest is therefore a policy of first importance to a public man. -
將在適當的時候加以說明的，乃是這一數字的來源。
It is how this number is known that will be described in due course. -
我遇到她乃是上上個禮拜。
It was the week before last that I met her.
