We want to convert a lowercase character to uppercase.
(a) String.toUpperCase() → This converts an entire string to uppercase, not a single char.
(b) Character.isUpperCase(char) → This checks if a character is uppercase; it does not convert it.
(c) Character.toUpperCase(char) → ✅ This converts a single character to uppercase.
(d) toUpperCase() → This is incomplete; we need the class or object it applies to.
Answer: (c) Character.toUpperCase(char)