D. Is a fly shot effective in preventing the flu?
Answer A touches on the topics of economics and industrial feasibility of the flu shot.
B is more of an ethical / situational question.
C is a social question.
D is the only question which focuses on the science of microbiology and medicine.
For a closed system, you need two things:
1) a conservation of mass within the boundaries of the system
2) the ability to freely exchange energy to & from the "closed" system with a surrounding external system
So, the answer is <u><em>never</em></u>, since your defining the "system" as the water within the bathtub, and an open bathtub is exposed to evaporation, which is not conserving mass within the defined "system".
The sun heats up the atmosphere at the equator. The dense water sinks under and forms deep water masses under the ocean current. Then it gets wind due to the air current and this brings currents at the surface if the ocean.
Answer:
The answer is: 
Explanation:
Scientific notation is of the kind: 
The given calculation:
Therefore, the answer in scientific notation is:
They help keep track of notes and experaments
