In regular expressions, what does the ? quantifier indicate?

• A. One or more times
• B. Matches any single character
• C. The preceding element is optional
• D. Marks the start of a line

Answer: (C)

The ? after a character or group makes that element optional, meaning it can appear either zero or one time in the match. This lets patterns accept both possibilities. For example, colou?r matches both color and colour because the u is optional. Similarly, ab? can match a or ab. This is distinct from other quantifiers: + requires one or more occurrences, * allows zero or more, and the dot is a wildcard that matches a single character (not a quantifier itself). The ? can also influence quantifiers to be non-greedy when used after them, but in its basic form it signals optional presence.