Bad teeth can be painful and even be deadly. Infections of the gums(牙龈) and teeth can release bacteria into the blood system. Those bacteria can increase the chance of a heart attack or stroke and worsen the effects of other diseases. And adults are not the only ones at risk. For example, a 12yearold boy died when a tooth infection spread to his brain in 2007 in Washington. Experts said it might have been prevented had he received the dental care he needed.
Experts say good dental care starts at birth. Breast milk, they say, is the best food for the healthy development of teeth. Breast milk can help slow bacterial growth and acid production in the mouth. But dentists say a baby's gums and early teeth should be cleaned after each feeding by using a cloth with a little warm water. Experts say if you decide to put your baby to sleep with a bottle, give only water.
When baby teeth begin to appear, you can clean them with a wet toothbrush. Dentists say it is important to find soft toothbrushes made especially for babies and to use them very gently. The use of fluoride(氟化物) to protect teeth is common in many parts of the world. For example, it is often added to drinking water supplies. The fluoride mixes with enamel(釉质), the hard surface on teeth, to help prevent holes from forming.
But young children often swallow toothpaste when they brush their teeth. The American Academy of Pediatric Dentistry notes that swallowing fluoridated toothpaste can cause problems. So young children should be carefully watched when they brush their teeth. And only a small amount of fluoridated toothpaste, the size of a pea, should be used.
Parents often wonder what effect finger sucking might have on their baby's teeth. Dental experts generally agree that this is fine early in life. Most children stop sucking their fingers by the age of four. If it continues, experts advise parents to talk to their children's dentists or doctors. Because it could interfere_with the correct development of permanent teeth.
Dentists say children should have their first dental visit at least by the time they are one year old. They say babies should be examined when their first teeth appear—usually at around six months.
According to the passage，what is the function of fluoride?

A．Making the surface on teeth much cleaner.

B．Protecting gums from being infected.

C．Keeping holes on teeth from forming.

D．Slowing down bacterial growth and acid production.

The underlined phrase “interfere with” in Para.5 probably means “________”．

A．do harm to	B．account for
C．contribute to	D．stand for

What is the purpose of the author in writing the passage?

A．To warn us of the deadly infections of gums and teeth.

B．To introduce the advantages of fluoridated toothpaste.

C．To draw our attention to the dental care of young children.

D．To present the research results about dental care.