题目

   In recent years, stress   61  (regard) as a cause of a whole range of medical problems, from high blood pressure to mental illness. But like so many so other things, it is only to much stress   62   does you harm. It is time you considered that it there were no stress in your life, you would achieve a little. If you are  63  (stick) at home with no stress, then your level of performance will be low. Up to a certain point, the more stress you are under, the  64  (good) your performance will be. Beyond a certain point, though, further stress will only lead to  65  (exh如图，在正方体中，M，N，G分别是，，AD的中点，求证：（1）MN//平面ABCD；（2）MN⊥平面．