Many students write to Language Doctor to _______ advice about learning English.

中国成语蕴涵着丰富的辩证法思想，下列成语中体现辩证否定原理的是（  ）

①古为今用，洋为中用         ②百尺竿头，更进一步

③冰冻三尺，非一日之寒       ④弃其糟粕，取其精华

设斜率为2的直线l过抛物线y²=ax（a＞0）的焦点F，且和y轴交于点A，若△OAF（O为坐标原点）的面积为4，则抛物线的方程为____ 

阅读理解

    If you want to live longer and lower the risk of heart disease, a move to the mountains may help. Research by scientists in Greece shows that living in the mountains is good for the heart and longevity(长寿). People living at higher altitude(海拔) have lower possibility of dying from heart disease than those closer to sea level, even if they have factors that could increase their risk. "Residence in mountainous areas seems to have a 'protective effect' from heart disease," said Dr Nikos Baibas of the University of Athens. He and his colleagues suspect that the increased exercise from walking up mountainous area gives the heart a good workout and enables it to cope with lower levels of oxygen.

    Researchers studied the health records and death rates of 1,150 Greeks who lived in three villages near Athens over 15 years. One village was 1,000 meters above sea level and the other two were in low-lying areas. Although men and women living in the mountainous village had higher blood pressure rates and other risk factors than people in the other villages, they had a lower rate of death from heart disease and other causes after a fifteen year follow-up." The contrast was more evident among men than among women," Baibas added in a report in the Journal of Epidemiology and Community Health. Heart disease is one of the world's top killers. Smoking, high blood pressure, raised cholesterol levels, being overweight and a family history of the illness increase the possibility of developing the disease.