I believe it is B. Thermosphere
Correct me if wrong.
The arrows usually point to the organisms that are doing the eating.
Explanation:
For that reason, we can say that the arrows represent the flow or transfer of energy in an ecosystem. It also specifies the direction of the flow of energy.
The flu vaccine changes every year. The flu vaccine is based on a predicted strain that is anticipated to be the most infectious that year. Thats why people who sometimes get the vaccination still get the flu, they don't have the antibodies for the strain they were infected with. Strains for viral disease don't change very much and usually the vaccination for them cover them well.
C) a system is a set of parts that function together as a whole