now and then 時而,不時（置于句尾）
e.g.He went to see his grandmother every now and then.
他時而去看看他的祖母.
now and again 時而
e.g.He chops in now and again.
他不時插一兩句話.
once in a while 偶爾,有時(置于句尾）
e.g.He comes to see me once in a while.
他現(xiàn)在是偶爾來看看我.