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.
