List<string> words = "This is a testing text.".Split(' ').ToList(); // Get each word.
List<string> blackList = new List<string>(); // Fill this.
List<string> whiteList = new List<string>(); // Fill this.

List<string> whiteListed = (from i in words where whiteList.Contains(i) select i).ToList();
List<string> blackListed = (from i in words where blackList.Contains(i) select i).ToList();
if (blackListed.Count == 0 && whiteListed.Count > 0)
{
      // It has a whitelisted word and not a blacklisted one.
      // Use 'whiteListed' in order to access the words which triggered the function.
}