懂你英语流利说Level4－Unit1 3/4 Vocabulary

A dental  cavity is a hole in a tooth.

A cavity is caused by bacteria in the mouth.

Brushing your teeth frequently and regularly can help prevent cavities.

A cracked tooth can be caused by biting down  and something hard .

Dentists often inject something into the gum to block the pain during the extraction process. 

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 the teeth and gums.

Braces are used on people with crooked teeth or after an injury.

Braces are used by dentists to straighten teeth over a period  of years.

The braces are usually for children they can also be used for adults with  crooked the teeth.

To extract a tooth means to remove it from the mouth.

Dentist have to pull hard to extract tooth.

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The  heart pumps blood to all parts of the body through a system of arteries and veins. 

It's located in the cheast  between the lungs and beat about 1 second .

The kidneys remove waste and toxins from the blood.

They are been ship on  and about 10cms long and 6cms wide.

The  lungs can exchange oxygen from the air with carbon dioxide from the blood  .

The expend when inhaling air and contract when exhaling air.

The stomach  is below the heart and is part of the disgestive system.

It uses acids to digest food before passing it to the small intestine.

The bladder is a ballon-shaped organ that collects urine from the kidneys.

In an adult,the bladder can hole about half a liter of urine.