A、Improper foods. B、Strong cleaning products. C、Nervous tension. D、Not mentioned in the passage. D本题问的是根据研究者的观点，痤疮是由什么引起的。短文中提到，

(22)Skin is the largest organ of the body. It is the body’s first barrier to infection. It keeps out many harmful bacteria and other things. It also keeps all the things we need in our bodies. The skin helps control body temperature. Glands(腺体)on the skin release fluid to cool the body when it gets too hot. When a person gets too cold, blood passages in the skin become narrow. This helps trap heat inside the body. Like other organs of the body, skin can also have problems. Almost any teenager can tell you the most common disorder: acne, which is connected to hormones and how they affect the oil glands of the skin. Some people think eating chocolate or oily foods causes acne. Others blame dirty skin or nervous tension.(23)Yet researchers tell us none of these causes acne. And skin experts say there are simple ways to help prevent acne. One is to touch your face as little as possible, so as not to add oils or put pressure on the skin. Another good idea is to avoid the urge to burst pimples(疙瘩). This can leave permanent marks on the skin. Doctors also say you should avoid strong cleaning products,(24)and be gentle as you wash and dry your skin.(25)However, there are kinds of skin problems which are far more serious than acne.
22. What message does the speaker want to convey at the beginning of the passage?
23. What causes acne according to researchers?
24. Which is the right way to prevent acne?
25. What is probably going to be discussed in the following passage?