Which of the following sentences includes a non-restrictive clause?
a Alan discovered that chickens are able to recognize the faces and voices they see and hear often.
b Giana, who collects anything relating chickens, found the perfect life-sized chicken hat to add to her collection.
c Roosters have an internal clock that causes them to crow at daybreak.
d The chicken gained quite the social media following after being featured in a video wearing a tutu while dancing.