Challenge 2: The Same Query, Two Different Results — Possible Solution
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Program.cs:

var numbers = new List<int> { 1, 5, 10, 15, 20 };
int threshold = 8;

var query = numbers.Where(n => n > threshold);   // captures threshold LIVE, by reference

Console.WriteLine("First enumeration (threshold = 8):");
foreach (var n in query) Console.WriteLine(n);

threshold = 17;   // reassigned AFTER the query was defined

Console.WriteLine("Second enumeration (threshold = 17):");
foreach (var n in query) Console.WriteLine(n);

Output:

    First enumeration (threshold = 8):
    10
    15
    20
    Second enumeration (threshold = 17):
    20

Explanation:
Because C# lambdas capture the variable itself rather than a snapshot
of its value at the moment the lambda was written, `query` doesn't
"remember" threshold as 8 forever. Each enumeration re-runs the
Where() predicate fresh, reading whatever threshold's CURRENT value
is at that exact moment. The first foreach runs while threshold is
still 8; the second runs after it's been reassigned to 17 -- same
query variable, same underlying Where() call, genuinely different
results.

WHY THIS WORKS AS AN ANSWER
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This demonstrates the chapter's own live-capture claim directly: the
exact same query object produces two different outputs across two
enumerations, purely because the captured variable changed in
between -- something java2-3's effectively-final rule would never
allow to even compile in Java.