Which of the following pulp horn of primary molar is commonly exposed during restorative procedures:

The mesiobuccal pulphorn of permanent maxillary 1st molar is commonly exposed during cavity preparation. Mesiolingual pulphorn of permanent mandibular 1st molar is commonly exposed during cavity preparation. Mesiobuccal pulphorn of primary 1st molars is commonly exposed during restorative procedures on primary molars.