To answer this question, let's go through each option to understand why it is correct or incorrect:
Option A) compile time error at line 1 - This option is correct because the code tries to call the length method on the a1 array, which is incorrect. In Java, arrays do not have a length() method. Instead, the length of an array can be accessed using the length field without parentheses. Therefore, there will be a compile-time error at line 1.
Option B) compile time error at line 2 - This option is incorrect. The code correctly accesses the first element of the a1 array using the index 0.
Option C) compile time error at line 3 - This option is incorrect. The code correctly prints the reference to the a1 array.
Option D) Runtime exception - This option is incorrect. There are no runtime exceptions in the given code.
The correct answer is A) compile time error at line 1. This option is correct because the code tries to call the length method on the a1 array, which is incorrect. Arrays in Java do not have a length() method.