a __bar_ of soap
three_pairs_of trousers
two__ boxes_of chalk
a_cup_of water
eleven __bottles__of milk
a_tin__of cola
two__ton_of stones
a _drop__of rain
eight_blocks__of ice
four_loafs__of bread
six_pound_of meat
seven_pieces__of paper
a_couple__of days
a__group _of students
我个人觉得,石头和冰块那两题可以互换.