Q5

A star cluster is a group of stars that form at the same time. Hertzsprung–Russell diagrams for three star clusters, $X$, $Y$ and $Z$ are shown.

Which row of the table correctly shows the three star clusters from youngest to oldest?
A. Youngest $Y$, then $X$, then oldest $Z$
B. Youngest $Y$, then $Z$, then oldest $X$
C. Youngest $Z$, then $X$, then oldest $Y$
D. Youngest $Z$, then $Y$, then oldest $X$