Quick challenge #2: how to truncate a string in C# and keep word boundaries (do not split a word in two)

[Q] How to truncate a string in C# with more than 10 characters and keep word boundaries (do not split a word in two)?

[Examples] "Good morning test." -> "Good morni..." (wrong), "Good morning..." (correct)

Quick challenge C#: how to truncate a string with more than 10 characters by adding an ellipsis to its end?

[Q] How to truncate a string with more than 5 characters by adding an ellipsis to its end?

[Example] "1234567" -> "12345..."