What told you the girl would be going to a dance? (7,4)
I believe the answer is:
crystal ball
'what told you the girl' is the definition.
I can't tell whether this definition defines the answer.
'would be going to a dance?' is the wordplay.
'would' becomes 'crystal' (I can't explain this - if you can you should give a lot more credence to this answer).
'be going to' means one lot of letters go next to another.
'a dance?' becomes 'ball' (ball is a kind of dance).
'crystal'+'ball'='CRYSTAL BALL'
Can you help me to learn more?
(Other definitions for crystal ball that I've seen before include "Fortuneteller's globe" , "Means of telling the future" , "Fortune-teller's essential equipment?" , "see the result first in here?" , "Glass globe" .)