The following text is for questions 14 - 18.

    Leeches are slimy worms with two suckers. The big one is placed at the rear end and a smaller one at the mouth. The leeches are able to expand their bodies since they have powerful muscles. Most leeches eat the blood of other creatures. A leech attaches itself to its victim by piercing its skin and secretes a substance which prevents the blood from clotting. Then it sucks up the blood. As it sucks, it expands so many times its normal size. Once a leech attaches itself to its victim, it is very difficult to remove. However, if you put salt on it, it soon falls off and dies.

    There is one species of leech that sucks animals' blood by entering their breathing passages. Later, the breathing passage will be completely blocked and make the victim suffocate.

    Many years ago, people believed that some diseases were caused because a patient had too much blood in his/her body Doctors would then attach leeches on to the patient. Some leeches, in fact, were specially bred for this purpose.

Which of the following statement is NOT TRUE ?