<prompt> A characteristic feature of lingual surface of the mandibular first premolar is:Rudimentary lingual cuspMesial marginal ridgeMesiolingual developmental grooveLingual triangular ridge  <response>: A characteristic of the lingual surface of the mandibular first premolar is the mesiolingual developmental groove. This groove acts as a line of demarcation between the mesiobuccal lobe and the lingual lobe and extends into the mesial fossa of the occlusal surface. 