That's not good enough, I more powDerful.
If it was a worksheet, I'd soak it in the water, then say, it
rained yesterday, and I couldn't see what's on the worksheet,
because I dropped it on the floor..... 
Next, if I need to complete it on a foolscap paper, I'd just take
any maths exercise I did a year ago and soak it in the water or ask
my dog to bite it into pieces, or put it in the washing machine and
tmr show the teacher, IT WASN'T MY FAULT.
