Correct Answer: Essential

Solution : The correct choice is the f irst option .

The term essential refers to something that is necessary or fundamental, without which something may not function properly or as intended. It is the correct synonym for the word requirement, which means a thing that is needed or wanted.

The meanings of the other options are as follows:

• Serious: Something that is serious is significant, important, or grave in nature.
• Vague: Vague refers to something that is unclear, imprecise, or not well-defined.
• Importance: Importance indicates the quality of being significant, valuable, or having great relevance.