Let's carefully analyze:
We have a string array String s[]. We want the number of elements in the array.
(a) s.length → ✅ Correct. For arrays in Java, .length without parentheses gives the number of elements.
(b) s.length() → ❌ Incorrect. length() is used for String objects, not arrays.
(c) length(s) → ❌ Not valid in Java.
(d) len(s) → ❌ Python syntax, not Java.
Answer: (a) s.length