In medicine, depending on the pathogens that cause colds, colds can be divided into viral colds and bacterial colds. If there is no bacterial infection, the cold can heal itself in about a week through the body's own immunity. So, most Colds do not require medication or injections. In order for the above conclusions to be true, which of the following must be true? ['Having a common cold is good for improving the immune system.', 'The common cold that people suffer from is viral influenza.', 'Taking medications and injections to treat diseases has major side effects on the human body.', 'Cold is not just virus cold and bacterial cold.']