Most Mornings,Becky Listens to Her Favourite Song as She Gets

Most mornings,Becky listens to her favourite song as she gets ready for work,including putting in her contact lenses.One afternoon,Becky hears her favourite song playing,and her eyes start watering-something that usually only happens when she puts in her contacts.If this is an example of classical conditioning,what is the unconditioned stimulus?

A) eye watering
B) Becky's contacts
C) the song
D) getting ready for work