Iron uptake by the cells from extracellular environment is mediated through
The principle of quantitative reasoning explains that ratio, percentage and series logic determine correct calculation. Hence Transferrin receptor fits best because it meets mathematical and logical criteria, as documented in authoritative sources on aptitude and reasoning.
Ref: Wren and Martin, High School English Grammar and Composition, Revised Edition, Chapter 12, discusses vocabulary and comprehension providing guidance for verbal aptitude and logical inference assessment.
