Determine which seed will germinate first
You'd have to know the individual germination times for each family.  I'm linking a table for vegetables, but it doesn't include the three plants you're looking at.  A google search for each one individually shows that yes Mung does have the shortest germination time.  It's a memorization question.

To add to that here is a paper where they review variation times between over 600 seeds and find that the variation in time is mainly constrained within families.