user
there was a boy who invited a friend over to play.  the mum said "im going to go to the shops now".  so she did.  the kids played footy inside.  when mum got home and said "you have been playing football haven't you?" How did she know??
A: cradle
B: cut
C: glass was on outside
D: window was open
E: ground was wet
assistant
<|begin_of_thought|>

Deep Thought is thinking for 7.5 million years.

<|end_of_thought|>

<|begin_of_solution|>

C

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