Wisdom teeth are normally the last teeth to appear. This usually happens when people are in their late teen years or early twenties--in other words, when they are older and wiser. Wisdom teeth are chewing teeth, at the back of the mouth. They can grow into place normally and never cause a problem. But often there is not enough room for them in the mouth. They might crowd other teeth. Sometimes they even push sideways through the gums( 牙床 ). An impacted wisdom tooth is one that fails to completely rise through the gum--the term is erupt. Wisdom teeth that only partially erupt can leave space for bacteria to enter around the tooth. Infection is a risk in these cases. Wisdom teeth that are not well in place and become impacted are often removed. People should have the placement of their wisdom teeth examined between the ages of sixteen and twenty. X-rays can show wisdom teeth that are below the gums. The American Dental Association says removal is generally advised when wisdom teeth only partly break through the gums. Removal is also advised if there is a chance that poorly placed wisdom teeth will damage other teeth. And removal is called for in cases where fluid collects around a wisdom tooth that is partly or fully below the gum. But why do we have wisdom teeth if we often need to get them removed?One theory has to do with our diets. Scientists say the diet of prehistoric humans probably required more chewing teeth. Life was probably a little rougher on the teeth back then, too. So it was good to have extras. The American Association of Oral and Maxillofacial ( 上颌面的 ) Surgeons says young adults are the best candidates for wisdom teeth removal. The group says older patients may be at greater risk for disease in the tissue surrounding the teeth. After surgery, there can be swelling of the gums and face and some pain.Both can be treated with cold wraps and medication( 药物治疗 ).1.[单选题]When a wisdom tooth fails to rise completely,_____.A.it may need more time to growB.it may cause swelling in the faceC.it may cause infectionD.it may be left unnoticed2.[单选题]The term quot;eruptquot; in this passage probably means_____.A.a tooth suddenly appearsB.a tooth rises through the gumC.a wisdom tooth suddenly cause a problemD.a wisdom tooth fails to rise completely3.[单选题]Humans have wisdom teeth probably becauseA.our ancestors needed to chew more when they grew upB.our ancestors#39; teeth grew at late teens or early twentiesC.our ancestors ate foods without cookingD.our ancestors had very tough lives4.[单选题]The problem wisdom teeth should be removed early, becauseA.older patients will feel more painB.older patients may face more serious problemsC.wisdom teeth are easier to be removed at young ageD.young people have stronger resistance to diseases5.[单选题]Wisdom teeth will cause problem when_____.A.they are below the gumsB.they have erupted from the gumsC.they don#39;t have place to grow normallyD.people are at their late teens or early twenties