The answer is c. Good luck ;)
I believe it is a, but I am not sure.
Sorry if I am wrong
Helium makes very light than hydrogen
Organisms adapt to their changing environment. When there is some pressure in the environment (for example, increased competition for food), then species with the most advantageous adaptations will survive. Because environments change pretty frequently, the organisms living there must cope with this change. This leads to ever changing and evolving species and increased biodiversity. Lastly, a high level of biodiversity leads to a healthy ecosystem because of the vast variety of organisms in that space. Many species allows niches to overlap and therefore no one organism occupies one niche.
