The answer is: A
Explanation
The correct option is A: 21 days.
This is because Section 171 of the Companies Act, 2013 states that a general meeting of a company may be called by giving not less than twenty-one days' notice in writing. This is the minimum period of notice required for convening a general meeting, unless a shorter notice is agreed upon by the members as per Section 101 of the Act. The notice should specify the date, time, place and agenda of the meeting, and should be sent to every member, legal representative of any deceased member, auditor and every director of the company. The purpose of giving a notice is to enable the members to attend and participate in the meeting and exercise their voting rights.