Vitamin D is necessary for health and growth．It is used by the body to form．strong bones and teeth．That is why growing children need it.
Vitamin D is also called the sunshine vitamin．It forms when the skin is exposed to the sun．In the past people Blew what vitamin D was they learned that sunshine was important．Poor children lived in crowded slums (贫民窟)．And they were often ill with tickets (软骨病) ．In Englad a tax was once placed on windows．Builders put few windows in houses．Rickets became so common that it was called the English disease.
Because s have reached full growth, they probably__________.