Answer:
Bacteria cause tooth decay
Step-by-step explanation:
Let's go through all of the answer choices:
"my dog is better than your dog" this is an opinion and it cannot be proven using the scientific method
"bacteria cause tooth decay" this can be proven using the scientific method, as we can test if bacteria actually causes tooth decay
"that is a beautiful flower" this is another opinion and cannot be proven using the scientific method as different people have different opinions
"apples taste better than bananas" this is yet another opinion and cannot be proven because some people may like bananas better and others may like apples better.
Therefore the answer is "bacteria cause tooth decay"