vaccines are weakened viruses or bacteria that prompt the body to develop antibodies to foght against disease
Explanation:
the last option is the correct answer
you see katie helped sandra with homework, which helped sandra not fail. Because katie did not let sandra fail, sandra can graudate and get a job. She can also thank katie for not letting sandra fail and go homeless.
sandra helped katie rollerblade. which has no significant impact. Who cares about rollerblading.
your answer is C