Does every assembly that you create have a reference to the mscorlib.dll assembly?

No. Although by default every assembly will have an automatic reference to the mscorlib.dll assembly, there is a compiler flag that can prevent this. For details, visit:

https://msdn.microsoft.com/en-us/library/fa13yay7.aspx

What is the maximum number of characters that can be stored in a string variable?

The maximum size of a string variable is 2 GB or about 1 billion characters because each char variable uses 2 bytes due to the internal use of Unicode (UTF-16) encoding for characters.

When and why should you use the SecureString type?

The string type leaves text data in memory for too long and it's too visible. The SecureString type encrypts the text and ensures that the memory is released immediately. WPF's PasswordBox control stores the password as a SecureString variable, and when starting a new process, the Password parameter must be a SecureString variable. For more discussion, visit:

http://stackoverflow.com/questions/141203/when-would-i-need-a-securestring-in-net

When should you use a LinkedList<T> variable?

Each item in a linked list has a reference to its previous and next siblings as well as the list itself so should be used when items need to be inserted and removed from positions in the list without actually moving the items in memory.

When should you use a SortedDictionary variable rather than a SortedList variable?

The SortedList class uses less memory than SortedDictionary, SortedDictionary has faster insertion and removal operations for unsorted data. If the list is populated all at once from sorted data, SortedList is faster than SortedDictionary. For more discussion, visit:

http://stackoverflow.com/questions/935621/whats-the-difference-between-sortedlist-and-sorteddictionary

Why should you not use the official standard for e-mail addresses to create a regular expression to validate a user's e-mail address?

The effort is not worth the pain for you or your users. Validating an e-mail address using official specification doesn't check whether that address actually exists or whether the person entering the address is its owner. For more discussion, visit:

http://davidcel.is/posts/stop-validating-email-addresses-with-regex/

http://stackoverflow.com/questions/201323/using-a-regular-expression-to-validate-an-email-address