1. The problem asks: What is d? However, the description provided is of a diagram involving shapes labeled A, B, C, D, and an enzyme, but no explicit mathematical expressions or equations are given. 2. Since there is no mathematical context or formula related to "d" in the description, it is impossible to determine what "d" represents or calculate its value. 3. To solve for "d", we would need additional information such as a formula, equation, or numerical data involving "d". 4. Without such information, the question "What is d?" cannot be answered mathematically. Final answer: Insufficient information to determine d.