This image depicts a cross section of the human eye. Which structure changes shape to focus incoming light? 
Definitions:
Marginal Cost
The rise in cost due to the production of an extra unit of a product or service.
Marginal Benefit
Marginal benefit refers to the extra benefit received from the consumption or use of an additional unit of a good or service.
R&D Spending
R&D Spending refers to the money allocated by businesses or governments towards research and development of new products or services.
Interest-Rate Cost-Of-Funds
The interest rate that banks and other financial institutions charge each other for loans, often used as a benchmark for other interest rates.
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