Hello! The best answer would be C - Colds because bacteria can reproduce and spread rapidly, which is why a cold sometimes develops fast. As for the others, your body is just adjusting to the weather with A, B is a sexually transmitted disease which is caused from contact with another through sex, D is caused by sweets/certain foods that break down your teeth. I hope I helped you!! Have a great day!!
Answer:
They speed up chemical reactions. Without them you wouldn't be alive. They break down macromolecules, and also lower the amount of energy needed for a chemical reaction to happen.
The skeletal system does not digest. That is the job of the digestive system. Hope this helps!
Years would be the independent variable because any sort of time is usually the independent variable.
