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が不可欠だ

is essential

→ が
phrase Rare #34,584
is essential Follows a noun; が marks the thing that is essential.
JA: 健康を保つには、十分な睡眠が不可欠だ。
EN: Getting enough sleep is essential for staying healthy.

私達が成功するには君の助力が不可欠だ。

Your help is essential for us to succeed.

生きていくのにはどうしても眠ることが不可欠だ。

Sleep is absolutely essential for staying alive.