1. all----not all/some---none/always----not always/sometimes----never/everywhere---not everywhere/somewhere---nowhere/only one, exactly one---none, more than one/at least one, some---none
2.对于选项为条件句，将必要条件取非。
if you get a high score of GMAT, you will be accepted by Harvard University.
取非为：if you get a high score of GMAT, you will NOT be accepted by Harvard University