What is the meaning of ‚Äö√Ñ√∂‚à ö√ë‚à ö‚à ´NULL‚Äö√Ñ√∂‚à ö√ë‚à öœÄ in Mysql?

• A. Not applicable
• B. Value not yet known
• C. Value undefined
• D. All of the mentioned