阅读下面短文，按照句子结构的语法性和上下文连贯的要求，在空格处填入一个适当的词或使用括号中词语的正确形式填空，并将【【答案】】填写在答题卷标号为16-25的相应位置上。
Vitamins are complex chemical substances 16        (find) in many foods.  The human body needs them for health and 17         (grow).  The body makes some vitamins, 18  usually in amounts too small to meet its needs. 19         vitamins are not made in the body.  These must be supplied.  No one knows exactly 20        all vitamins work.  Doctors 21    know that vitamins have very special uses.  One vitamin 22        cannot take the place of another.  The steady absence of one vitamin in 23       otherwise complete diet causes a deficiency disease.  Rickets, scurvy, and pellagra are examples of deficiency diseases.
It is best to obtain vitamins 24       eating the foods in which they occur.  There are also pills that contain a single vitamin or a combination of vitamins.  People should consult 25       doctors before they take any vitamin pills.