? ? cavity n.腔送漠，洞;蛀牙，齲洞
A dental cavity is a hole in the tooth. A cavity is caused by bacteria in the mouth. Brushing your teeth frequently and regularly can help prevent cavities.
? cracked? ? adj.有裂縫的;聲音沙啞的;精神失常的
v.破裂;崩潰(crack的過(guò)去分詞);發(fā)沙啞聲
A cracked tooth can be caused by biting down on some hard. Dentists the treat cracked tooth by covering it with a crown(牙冠).
? crown? ? n.王冠;花冠（有時(shí)象征勝利）;王權(quán);（某物的）頂部? vi.露頂
vt.（尤指通過(guò)增添成就无畔、成功等）使圓滿;為…加冕;使圓滿完成;給…以榮譽(yù)
A dental X-ray is a picture of your teeth and gums. An X-ray shows what can’t be seen on the surface of teeth and gums.
Braces are used by dentists to straighten teeth over a periods of years. Those braces are usually for children. they can also be used for adults with crooked teeth.
Brace? vt.支撐;系緊;準(zhǔn)備，預(yù)備;振作起來(lái)? vi.準(zhǔn)備好;支持;打起精神
n.支持物;鐵鉗吠冤，夾子;[語(yǔ)]大括號(hào);繃緊（身體部位的）肌肉
Straighten? vt.& vi.變直檩互，把…弄直;整理，整頓;使…改正;使…好轉(zhuǎn)
vi.變好起來(lái)
crook? ? n.騙子;彎曲;鉤;詭計(jì)? vt.使成鉤狀;使彎曲
vi.彎曲? ? ? adj.不正當(dāng)?shù)?騙人的
crooked? ? adj.彎曲的;不正當(dāng)?shù)?歪扭的;用不正當(dāng)手段得來(lái)的
To extract a tooth means to remove it from the mouth. Dentists have to pull hard to extract a tooth.
The heart pumps blood to all parts of bodies through a system of arteries and vein.? It’s located in the chest, between the lungs and it beats about once per second.
Artery? n.[解剖]動(dòng)脈;干線咨演，要道
toxin? ? n.毒素;毒質(zhì)
The kidneys remove waste and toxins from the blood. They have been shaped? and about 10 cm long, and 6 cm wide.
The lungs exchange oxygen from the air with CO2 from the blood. They expand when inhaling air and contract when exhaling air.
Inhale? ? vt.& vi.吸氣;吸入;〈非〉狼吞虎咽
Exhale? ? vt.發(fā)散出;放出闸昨，放射;使蒸發(fā);[醫(yī)]滲出
vi.呼氣;發(fā)散;放出
The stomach is below the heart and it’s part of the digest system. It uses acids to digest food before passing it to the small intestine.
Small intestine n.小腸
The bladder is a balloon-shaped organ that collects urine from the kidneys. In an audit, the bladder can hold about half a liter of urine.
urine? ? n.尿;小便;下泉
a liter of 公升
