Global cooling because it habitat was too cold and also there cooled blooded and so the change in temperature severely decreased their population so they died out.
C can be taken out of the question as eukaryotic cells do not have a nucleus. A lysosome is is only in prokaryotic cells so B can be taken out of the question. The answer should be D.
Answer: Covalent bonds form when atoms share their valence electrons with other atoms to become a more stable molecule.
Explanation: Atoms form covalent bonds as a result of the Octet Rule. The Octet Rule states that all atoms in a molecule need to have eight electrons in their valence shell. This rule can be satisfied by sharing, losing or gaining electrons. A covalent bond allows atoms to satisfy the Octet Rule via sharing.
Hasty generalization hope it helps
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