Task: Instance Class Understanding (ontology: Sciences/Computer_Science)

Which of the following classes does 'Low grade ovarian tumor' belong to as one valid explicit type? Context: A histologic grade for ovarian tumor according to a two-tier grading system indicating that the tumor is low grade.

A. clinical tumor stage group according to AJCC 7th edition
B. histologic grade for ovarian tumor according to a two-tier grading system
C. directive information entity
D. Karnofsky score vaue specification

Answer: histologic grade for ovarian tumor according to a two-tier grading system