Answer:
bird
tortoise
Explanation:
<em>"different </em><em>beak</em><em> shapes". </em>Beaks are often associated with birds.
<em />
<em>"with different </em><em>shells</em><em>". </em>From the phrase and the one before <em>(The same for tortoises.)</em>, it is clear tortoises are the main topic.
Answer: It helps chemists understand the world of chemical reactions and arranges all the elements in an organized manner.
Explanation: