Fulproof questions

• Why would you use an immutable value in a dictionary?
• How ToLookup() with multiple indexes?
• How to get the reference of TPL task's thread in C#?
• Can you advise me a resource with LINQ/lambda code exercises? [closed]
• What is the difference in .NET between developing a multithreaded application and parallel programming?
• How to sort in a WPF ListBox?
• What .NET 4.0 System.Collections.Concurrent collection added in functionality to .NET 3.0 SynchronizedCollection?
• Why is the Task's Result property unavailable for non-generic Task (C# 4.0+)?
• How to count the amount of concurrent threads in .NET application?
• When to use BlockingCollection and when ConcurrentBag instead of List<T>?

Fulproof answers