Step 1: Recall the two rival definitions:
Marshall (welfare-based) said economics studies mankind in the ordinary business of life; Robbins (scarcity-based) rejected the welfare criterion and focused purely on the logic of choice.
Step 2: Identify Robbins's key words:
His definition rests on three ideas: unlimited ends (wants), scarce means (resources) that have alternative uses, and the need to choose between competing ends.
Step 3: Match to the options:
Only "Science of scarcity" captures this ends-means-choice relationship; the other three options describe markets, business, or general life, none of which is Robbins's actual criterion.
Final Answer:
Option D, Science of scarcity.