Can ye pick the correct four?

In the upcoming second book, in the School for Swabbies series, Jack and his friends will be needin' to decipher the rhyme and push the four correct stones in order to be openin' the door to the chest containin' the.....(you'll be havin' to read the book to be findin' out :-) )....but until then ye can be havin' a crack at the puzzle. Based on the rhyme which four blocks should Jack be pushin'?