Most people associate tears with people who are crying because they are upset, angry or extremely happy, but there are actually

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问题       Most people associate tears with people who are crying because they are upset, angry or extremely happy, but there are actually three different kinds of tears.
      Firstly there are basal tears.These are tears regularly produced by the tear glands which are above your eyes, under the eyelids and protect the eyes by keeping them clean and wet.Basal tears are spread evenly over the eye by blinking.They are made up of a mixture of water, oil and mucus (粘液).

      But there are other tears which have no connection with emotions either.These tears also protect the eyes.So how are they different? The second kind of tears are called reflex tears and their job is to wash out.foreign objects that come into contact with the eye—when an eyelash or an insect gets stuck in your eye, for example.Reflex tears can also be caused by the smell of onions or smoke, which contain chemicals and tiny particles.In addition, cold air or wind, which dries out the eyes, causes the tear glands to produce reflex tears.In English we often say our eyes are "watering" when this happens.
      And then there are "real" tears—emotional tears.They are produced by emotional stress or pain and have been found to contain more hormones than other types of tears.Most mammals produce basal or reflex tears, but we humans produce emotional tears.
      Emotional tears and reflex tears also come from the tear glands.Some of the tears drain away through the tear ducts in the corner of your eyes.But when too many tears are produced, they roll down your face.Your tear ducts are also connected to your nose, which is why tears sometimes run down into it.Both reflex tears and emotional tears are more watery than basal tears.
      What, is the function of emotional tears? Studies indicate that our bodies use them as a way of re-establishing balance of the nervous system.They are a way for us to calm down after a period of stress.Research across cultures also indicates that emotional tears help people to establish a bond with people they care for.Tears express vulnerability and most people react with sympathy to tears.


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答案a mixture

解析 文章第二段末句提到,基底泪由水、油和粘液组成。故填入“a mixture”。
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