Never use “that” when referring to a person. This is a common mistake — one that I often find in my own writing during the editing stage. For example:
(wrong) The first person that walked on the moon was Neil Armstrong.
(correct) The first person who walked on the moon was Neil Armstrong.
(wrong) The teacher that she was referring to was Ms. Santorelli.
(correct) The teacher to whom she was referring was Ms. Santorelli.
People: who/whom. Non-people: that/which. Got it?
Okay, quick quiz. Which one is correct? Hmmm…
1. The student was indebted to the weekly writing tips from the author who helped improve her writing.
2. The student was indebted to the weekly writing tips from the author which helped improve her writing.
(Careful, this may be a trick question!)