<span>In the forest service, people from different occupational areas would work, with a broad sense of service to nature and conservation of the same, they have a mission to protect the earth and serve the people and the nation with honor and pride, feeling nature so unpredictable</span>
Every species exhibits variations based on various genes being activated at various times. An example with humans can be eye color or hair color. What species means is that all members of a species can procreate with healthy, capable of procreating progeny, but anything else is just a variation.
If a bacterium cannot use citrate agar will not change its color (stays green). On the other hand, if bacteria have the ability to use citrate, the medium will change its color from green to blue.
This happens because citrate agar contains pH indicator such as bromothymol blue which transforms from green to blue in alkaline conditions.
The answer is b. Hope this helps :)