Answer:
Option C i.e., Workflow is the correct answer to the following question.
Explanation:
The following option is correct because Workflow makes secure that field of amount that is populated when the Close Won stage is set. So, that's why the workflow meets the following necessity.
Option A is not true because there is no rules is validating.
Option B is not true because the following requirement is not meet the process of the Lightning Builder.
Option c is not true because there is not any requirement of process of the approval.