The given diagram shows different parts of human eye with one part labeled as X. Which the following statement is correct regarding label X?

• A. It is the opening in lens that permits light into the inner chambers of the eye.
• B. It is the coloured portion of vascular tunic.
• C. It is a biconcave structure that changes shape to bring objects into focus.
• D. It is thick, jelly-like substance in the posterior compartment of the eye.