This is the exact answer:
Bacteria are helpful because they produce oxygen, which our bodies need to breathe, and they help us to digest the food we eat. Bacteria are also helpful because they are used in medicine to help us overcome disease. Bacteria are harmful because they can cause tooth decay and illnesses that can be either common or quite serious.
Answer:
The answer is C.
Explanation:
At first, an enzymes called Helicase unwind the double helix in a DNA .
