阅读理解。 We all know that certain oils are healthier than others, but your oil health goes beyond just the type. The health of your oil can be related to how you use it too. Each type of oil has what is called a 'smoke point'. The smoke point is the specific temperature at which the oil starts to break down, or in more technical terms, its molecular structure begins to change. These molecular changes result in changes in flavor, as well as changes in nutritional value, specifically, the nutritional value of the oil starts to reduce; changing what once may have been considered an especially healthy oil, like Olive, into one that is unhealthy. The higher an oil's smoke point is, the higher the temperature of the oil can be. As a result, each type of oil should be used for the cooking method that is most appropriate to its individual smoke point and heat tolerance. Here is a quick guide for the next time you reach for your favorite oil. Note that the above table represents oils that are refined (精烁). Most oils we buy are refined. Refined oils tend to have much higher smoke points than when they are unrefined. They also differ in nutrition and flavor, Unrefined oils are more nutritious and they tend to be much richer in flavor. When it comes to extremely high heat cooking, always choose oils which are refined. 1. What determines whether an oil is healthy or not? [     ] A. Whether it's refined or not. B. Its smoke point. C. Its molecular. D. How you use it. 2. Which of the followjng might be a better choice to make a healthy salad? [     ] A. Refined walnut oil. B. Safflower oil. C. Unrefined olive oil. D. Sunflower oil. 3. Healthy oil can become unhealthy if _____ according to the passage. [     ] A. you keep it for too long B. it is heated well beyond its smoke point C. it is refined D. its flavor is changed 4. The author wants to tell readers that _____. [     ] A. oils are related to health B. oils'value depends on their smoke points C. 'certain oils are healthier' is relative D. oils' flavor and nutrition are connected