A
Blood brings oxygen and nutrients to all the parts of the body so they can keep working. Blood carries carbon dioxide and other waste materials to the lungs, kidneys, and digestive system to be removed from the body. Blood also fights infections, and carries hormones around the body.
Red blood cells are shaped like slightly indented, flattened disks. They contain hemoglobin, a protein that carries oxygen. Blood gets its bright red color when hemoglobin picks up oxygen in the lungs. As the blood travels through the body, the hemoglobin releases oxygen to the different body parts. Each red blood cell lives for about 4 months. Each day, the body makes new red blood cells to replace those that die or are lost from the body. They are made in the inside part of bones called the bone marrow(骨髓).
White blood cells are a key part of the immune system. The immune system helps the body defend itself against infection. Different types of white blood cells fight germs, such as bacteria and viruses. Some types of white blood cells make antibodies, which are special proteins that recognize foreign materials and help the body get rid of them. The life spans of white blood cells vary from hours to years. New cells are constantly being formed.
Blood contains far fewer white blood cells than red blood cells. But the white blood cell count in someone with an infection often is higher than usual because more white blood cells are being made to battle the infection.
Platelets (血小板)are tiny oval-shaped cells that help stop the bleeding. When a blood vessel breaks, platelets gather in the area and help seal off the leak. Platelets survive only about 9 days in the bloodstream and are constantly being replaced by new platelets made by the bone marrow.
【文章大意】本文是一篇说明文, 介绍了血液的构成及各部分的作用。
1. What causes the blood to take on bright red?
A. Bone marrow. B. Oxygen.
C. Carbon dioxide. D. Waste material.
【解析】选B。细节理解题。根据第二段中“Blood gets its bright red color when hemoglobin picks up oxygen in the lungs. ”可知, 当血液在肺里携带上氧气之后, 便呈现出深红色。故选B。
2. What will happen if your body has fewer white blood cells?
A. Your immune system will disappear.
B. Your body will be short of protein.
C. You will get infected more easily.
D. Your marrow will stop making blood.
【解析】选C。推理判断题。根据第三段可知, 白细胞是免疫系统的关键部分, 由此可推测, 如果血液里缺少白细胞, 那么人的免疫力会下降, 更容易被疾病感染。故选C。
3. What will help when you cut your finger?
A. Red blood cells. B. White blood cells.
C. Hemoglobin. D. Platelets.
【解析】选D。细节理解题。根据最后一段中“Platelets are tiny oval-shaped cells that help stop the bleeding”以及下文的内容可知, 血小板主要作用是止血。故选D。
