(a) Market price of a share / Earning per share.
P/E Ratio = Market Price per Share / EPS (Earnings Per Share).
Source: Profitability Ratios, Chapter 10
The P/E Ratio is a stock market-related ratio under Profitability Ratios. Examiners expect you to directly identify option (a) and optionally state the formula. Options (b) gives EPS, (c) gives Return on Capital Employed, and (d) gives Return on Shareholders' Equity — common distractors.