Answer:
Correct option is D: Community gardens began in 1998, which resulted in a positive environmental impact on neighborhoods across the nation.
Explanation:
The most format style of a sentences is shown in option D because it provides great meaning without too much full-stops and avoid parallel errors. In option A and B, there are too many stops and almost meaningless phrases standing alone. Option C would have been a good option, but using "so" after the comma and "worry about getting good" and "healthy stuff to eat" makes it informal.
NASCAR and boxing and your risking some concussions
No that is pretty irrelevant these days, sorry bro. <span />
the answer is A. Hamlet finally made a decision and acted on it
Hey!
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Part A:

When Samara came up with the idea of creating a new park she didn't know anything about how she would come up with an idea and presenting it to the zoning board.
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Part B:

What I said above is what the answer is to Part B. If Samara wouldn't have gone to the library to learn how you would present an idea to the zoning board she would have never been able to create the park at all.
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Hope This Helped! Good Luck!