The answer to your question is D. <span>. to protect students who cannot be vaccinated with herd immunity</span>
Smallpox<span> vaccine, the first successful vaccine to be developed, was introduced by Edward Jenner in 1796. He followed up his observation that milkmaids who had previously caught </span>cowpox<span> did not later catch </span>smallpox<span> by showing that inoculated</span>cowpox<span> protected against inoculated </span>smallpox<span>.</span>
Maybe when an organism has both an endocrine and a nervous system it is able to not only make rapid changes to be more well-adjusted in its enviroment but is also able to make changes required for survival in long-term.
