The correct answer would be C.seasonal changes in the amount of daylight. Since leaves require sunlight in order to perform photosynthesis to keep the tree alive, when seasonal changes occur where there is not enough sunlight throughout the day, trees go dormant for the season until conditions are right.
One is probably because your friend has a stronger immune system than you and is able t fight the bacteria infection. The other is probably that your friend is also infected but does not show any symptoms of the infection, in what is referred to as latent infection. The bacteria enters a lysogenic cycle in your friend’s body rather than the more virulent lytic cycle (that happens to you).
Answer: Oxygen
Explanation: There's no explanation to go with the answer, sorry.
Try researching the discovery of microscopes and their impact on scientific discoveries, including cells!!!