How can I split a string with a string delimiter?

.Split(new string[] { "is Marco and" }, StringSplitOptions.None)

Consider the spaces surronding "is Marco and". Do you want to include the spaces in your result, or do you want them removed? It's quite possible that you want to use " is Marco and " as separator...

string[] tokens = str.Split(new[] { "is Marco and" }, StringSplitOptions.None);

If you have a single character delimiter (like for instance ,), you can reduce that to (note the single quotes):

string[] tokens = str.Split(',');