The best answer for the underlined word would be A: Vital
crucial means important or urgent.
required could be it but it does not imply a great amount of necessity.
The rest of the options don't even relate to this question.
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But woo her, gentle Paris, get her heart,
My will to her consent is but a part;
An she agree, within her scope of choice
Lies my consent and fair according voic
The answer is C. because requisite is something that is required or necessary.
