To prevent a compile-time error, how should the following code be changed?

struct ListNode // Line 1 { // Line 2 intdataVal; // Line 3 NodeType* next; // Line 4 } // Line 5

1. Insert the following before line 1:

typedef ListNode* NodeType*;

2. the following before line 1:

struct ListNode;

typedef ListNode* NodeType*;

3. Replace line 4 with the following:

ListNode* next;

4. Either Insert the following before line 1:

typedef ListNode* NodeType*;

5. None of these answers is correct.