A 22 year old presents with a fracture of the incisal third of tooth 2.1 exposing a small amount of dentin. The fracture occurred one hour previously. There is no mobility of the tooth but the patient complains that it is rough and sensitive to cold. The most appropriate emergency treatment is to

smooth the surrounding enamel and apply a calcium hydroxide cement

smooth the surrounding enamel and apply glass ionomer cement.

open the pulp chamber, clean the canal and temporarily close with zinc oxide and eugenol

place a provisional (temporary) crown.