已知集合M={1,2,3,m},N={4,7,n4,n2+3n}(m、n∈N),映射f:y→3x+1是从M到N 的一个函数,则m-n的值为( )
( ) I can see ______ in Lucy's room.
( ) -- _______ are his football clothes? -- Under the bed.
( ) I have two good pen friends. One is an American, ______ is in England.
( ) There are so many people in the shop. You must ________ your things.
( ) -- __________? -- My bike is broken.