What is the result of the following code?

3: String s = "purr";
4: s.toUpperCase();
5: s.trim();
6: s.substring(1, 3);
7: s += " two";
8: System.out.println(s.length());

❌ A. 2
❌ B. 4
✅ C. 8
❌ D. 10
❌ E. An exception is thrown.
❌ F. The code does not compile

Explanation:
This question is trying to see if you know that String objects are immutable. Line 4 returns "PURR" but the result is ignored and not stored in s. Line 5 returns "purr" since there is no whitespace present but the result is again ignored. Line 6 returns "ur" because it starts with index 1 and ends before index 3 using zero-based indexes. The result is ignored again. Finally, on line 6 something happens. We concatenate four new characters to s and now have a String of length 8.