An Astronomer Plots the H-R Diagram of a Star Cluster

An astronomer plots the H-R diagram of a star cluster and finds that it contains hot B-type stars on the main sequence and cooler G- and K-type stars noticeably above the main sequence. This cluster is

A) of indeterminate age since the age of the cluster cannot be estimated from the information given.
B) impossible because cool stars cannot be above the main sequence when hot stars are on the main sequence.
C) old because the G and K stars are already evolving off (away from) the main sequence.
D) very young because the G and K stars are still evolving toward the main sequence.