C#.NET — ref, out, params, and performance claims: pick the correct statements. Which statements are correct? An argument passed to a ref parameter need not be initialized first. Variables passed as out arguments need to be initialized before being passed. An argument that uses the params keyword must be the last parameter.</br> Pass by reference can eliminate the overhead of copying large data items.</br> To use a ref parameter, only the calling method must explicitly use the ref keyword.

Introduction / Context:
This question tests knowledge of ref, out, and params in C#, along with a performance consideration about passing by reference for large data structures.

Given Data / Assumptions:

• Five statements covering initialization requirements, ordering constraints, and performance.

Concept / Approach:
Recall: ref requires the variable be definitely assigned before the call; out does not require prior initialization but the callee must assign before returning; a params parameter must be last; and pass-by-reference may avoid copying large structs or arrays (though real performance depends on context). Both declaration and call sites must use ref for ref parameters.

Step-by-Step Solution:

Verification / Alternative check:
Compile small examples showing the compiler errors when ref/out initialization rules are violated, and changing the order of a params parameter fails to compile.

Why Other Options Are Wrong:

• A/B include statement 2, which is false for out initialization rules.
• D includes 5, which is false.
• E is wrong because a valid grouping exists (3, 4).

Common Pitfalls:
Swapping ref and out rules, and forgetting that params must be last.

Final Answer:
3, 4