First Principles Thinking: Defining Gross Profit
C is correct. Gross Profit = Revenue - Cost of Goods Sold (COGS). The problem states Depreciation is included in COGS. This is a distractor or a clarification; if it's in COGS, it's already subtracted. Gross Profit = USD1,000 - USD600 = USD400. Gross Margin = 400 / 1,000 = 40%. SG&A is an operating expense, not part of COGS, so it is ignored for Gross Margin.
A is incorrect: This likely subtracts SG&A as well (USD1000 - 600 - 150 = 250/1000 = 25%), which is Operating Margin, not Gross Margin.
B is incorrect: This might attempt to add back depreciation (USD600 - 50 = 550 adjusted COGS), but if depreciation is a production cost, it belongs in COGS.