People, like all living things, need food．Food gives us the nutrients our bodies need．____1____ Energy is needed to carry out the life processes．
Our bodies cannot use the nutrients or energy in food unless the food is changed．The changing of food into a form the body can use is called digestion．
What does digestion do? _____2___ Digestion also changes the chemicals of food．It changes large, complex food molecules (微粒) into smaller, simpler ones．
____3____ Digestion takes place in the digestive tract．The digestive tract is a long, winding tube in your body．If stretched out, the digestive tract would be more than 9 meters (30 feet) long．
What are the parts of the digestive tract? The parts of the digestive tract are: the mouth, the foodpipe, the stomach, the small intestine(肠), and the large intestine．
There are many organs along the digestive tracts, such as the liver．____4____ The digestive tract and the other digestive organs make up your digestive system．
Food enters the body through the mouth．Waste materials (undigested food) leave the body through the anus(肛门)．The anus is at the end of the large intestine．
Digestion is a step-by-step process．____5____ It takes food from one to two days to pass through the entire digestive tract．
A．It also gives us energy．
B．It does not take place quickly．
C．Where does digestion take place?
D．Does the food also give us much strength?
E．Digestion breaks down large pieces of food into smaller pieces．
F．These organs are not part of the digestive tract, but they help in digestion．
G．Although they don’t belong to the digestive tract, they help us fight diseases．