Explanation
The MatchCollection.GetEnumerator method returns an enumerator that iterates through a collection.
Note:
The MatchCollection Class represents the set of successful matches found by iteratively applying a regular expression pattern to the input string.
Incorrect:
Not B: The ICollection.SyncRoot property gets an object that can be used to synchronize access to the ICollection.
Reference: MatchCollection.GetEnumerator Method
https://msdn.microsoft.com/en-us/library/system.text.regularexpressions.matchcollection.getenumerator(v=vs.11