For letter a, it is not advised to cut towards yourself. Although you might not harm the people surrounding you, you can't afford to risk yourself. For letter b, do not apply so much force. Just apply the minimal force, just strong enough to cut through. For letter c, you have to wear the goggles all the time for safety purposes. For letter d, I think this is the answer. When you only want to cut the skin, it would be better to use scissors.
Answer:
from what we see from the graph when the children had the 1st vaccine antibodies in the blood raised. then the concentration of the antibodies depleted, after the children had the second dose of the measles vaccine again, the antibodies in the children's blood raised drastically then the first dose.