Shown below is a free energy diagram representing a generic reaction of a substrate (S) to give a product (P), in the absence and presence of an enzyme.

Specific points on the free energy diagram are labelled A-D.

Free energy differences are labelled by arrows 1-14 on the right with the following colour code:

• Black: Transitions between S and P
• Red: Other transitions to/from S
• Cyan: Other transitions to/from P

[Note that a free energy difference is defined as the free energy of the destination (arrow head) minus the free energy of the origin (arrow tail)].

Which point represents the transition state of the enzyme-catalysed reaction?