The Choices Below Each Describe the Appearance of an H-R

The choices below each describe the appearance of an H-R diagram for a different star cluster. Which cluster is the youngest?

A) The diagram shows main-sequence stars of every spectral type except O, along with a few giants and supergiants.
B) The diagram shows main-sequence stars of spectral types G, K, and M, along with numerous giants and white dwarfs.
C) The diagram shows main-sequence stars of all the spectral types except O and B, along with a few giants and supergiants.
D) The diagram shows no main-sequence stars at all, but it has numerous supergiants and white dwarfs.