a. the production of bubbles by the plant when it is in darkness
Explanation:
The indirect observation that will show that the gas produced in this experiment is oxygen is by observing the bubbles on the surface of water in darkness.
Oxygen gas is a by product of photosynthesis. Photosynthesis occurs in the dark and when there is light.
If we observed the bubbles over water, it shows that oxygen gas is given off and the water plant is photosynthesizing. This is a good way to observe the oxygen gas indirectly.
Learn more:
Photosynthesis brainly.com/question/2761166
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I would say that the most likely answer is C.
While B and D could happen that are too vague and non-descript, A is completely wrong.
The answer is; When the planet is at A it is moving faster than at B.
This is because when the planet is closer to the sun at point A, it is experiencing a stronger gravitation, by the sun, pull than at point B. Therefore, its acceleration due to gravity at point A is higher than at point B.