Circulatory system.....circulates blood (a vital delivery system of oxygen) throughout the whole body when tissues need it the most and with a constant supply.
Answer:
b. They cannot reproduce outside of a host cell.
Explanation:
Viruses are <em>parasitic organisms</em> that need a<em> host</em> in order to<u> thrive</u> and <u>reproduce</u>. This means that they cannot replicate outside of a host cell, but can only do this by parasitizing it. They have to find a host cell in order to continue their life-cycle or else they won't thrive. The word "obligate" means <em>being restricted to a specific mode or function in life</em>. This shows that the virus has a restriction when it comes to <u><em>reproduction.</em></u> It cannot reproduce without finding a host cell.
