阅读理解。 Sometimes we cry because we are sad and sometimes because we are extremely happy. An irritant (刺激 物),such as onion (洋葱) smell or grains of sand in the eye,can also make cry. In this case tears perform an obvious role in getting rid of substances that might harm the surface of the eye. Dr. William Frey of the Dry Eye and Tear Research Center at St. Paul in Minnesota,USA,believes that tears from emotional causes may perform a similar role. He thinks that crying could get rid of emotional stress by washing away a chemical in the blood caused by strong emotions. To prove his theory, he hopes first to identify this chemical and then see if it is found in tears of sadness or happiness. So far, Dr. Frey has failed to find out the difference between emotional tears and tears caused by an irritant in the eye. This may be because these substances themselves cause a degree of stress and emotion. What he has identified in all tears is a variety of biochemicals (生化物) which are one of the causes of stress. A more detailed study may help us understand why sufferers from stress-related disorders cry less often than healthy people. Dr. Frey is also very interested to see if there are any physiological (生理学的) explanations for why women, in general, cry five times more often than men,on average. 1. The main purpose of Dr. Frey's study of tears is to _____. A. show that there are two types of tears,caused by irritants and by emotions B. find out the cause of stress-related problems and emotional disorders C. explain why women cry more often than men D. prove that tears can remove a chemical in the blood caused by strong emotions 2. Which of the following is true according to the passage? A. Tears fail to help get rid of emotional stress. B. Irritants in the eye result in tears without causing stress and emotion. C. Healthy people cry more often than those with stress-related problems. D. The biochemical identified by Dr. Frey has nothing to do with stress. 3. We can learn from the passage that _____. A. crying does us more harm than good B. inner feelings don't affect our bodies C. sorrow may cause some chemicals in our blood D. emotional tears are different from tears caused by irritants in the eye 4. Dr. Frey believes that tears from emotional causes may play a role in getting rid of _____. A. emotional stress by washing away a chemical in the blood B. onion smell or grains of sand C. sufferings from irritants D. substances that might not harm the surface of the eye