using the choice from one "select" choice to define another

[portablemarko]

Hi,
I'm trying to make a form that lets users book a class and time.
Is it possible to set up CK Forms to display a select box dependent upon the selection in another above it?
i.e. user chooses 'maths' from a classes field and is then only presented with the appropriate times for that class (maybe 12:30, 14:40 and 16:30) rather than all times for all classes, in a 'time' select box?
Thanks