smile from ear to ear
something you do when you are very happy
a piece of cake
something which is very, very easy
back to square one
start again when things don't go well
cross your fingers
something you do to get good luck
hit the books
study a lot
keep an eye on someone or something
check, investigate
saved by the bell
you can feel this at the moment you have to answer in class and the bell rings
under the weather
when you feel ill
when pigs fly
it will never happen
it costs an arm and a leg
very expensive
have a nap
to rest for a short time
as red as a beetroot
embarrassed
be the teacher's pet
being the teacher's favourite student
keep an eye on someone/ something
have a look
