To determine when the train is moving at a constant positive velocity, we need to look for intervals where the velocity graph is a horizontal line above the x-axis (indicating a constant positive velocity).
Given these criteria, we can analyze each option:
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A. 10-12 seconds: Check the graph in this interval. If it's not a horizontal line above the x-axis, this option is incorrect.
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B. 2-6 seconds and 12-14 seconds: Check both intervals for horizontal lines above the x-axis for positive constant velocity.
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C. 14-16 seconds: Check if this interval shows a horizontal line above the x-axis.
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D. 0-2 seconds and 6-10 seconds: Also, check if these intervals show constant positive velocity.
Once you've checked the graph, you can identify the correct intervals. The option with horizontal lines showing constant positive velocity in the graph indicates the correct answer.
Assuming the proper analysis of the graph:
If the intervals where the velocity is constant and positive were indeed identified in options B (2-6 seconds and 12-14 seconds), then option B would be the correct answer.
However, if no options fit, or you find that other intervals are indeed consistent with a constant positive velocity based on examination of the actual graph, adjust accordingly.