Question

1. why do animals need multiple systems to survive?

because one system can do everything
because each system does a different job and they work together
because their cells do not function alone
because their organs grow independently

Explanation:

In animals, different systems (like the circulatory, respiratory, digestive systems etc.) have specialized functions. For example, the respiratory system takes in oxygen and expels carbon dioxide, the circulatory system transports oxygen and nutrients. They work in a coordinated manner. One system cannot perform all the functions required for survival. Cells do function in a coordinated way within tissues, organs and systems, but the question is about systems. Organs are part of systems and do not grow independently in a functional sense for survival.

Answer:

Because each system does a different job and they work together.