Answer:
A) Convince neighbors to help you plant flowers in the park.
Step-by-step explanation:
This is the purpose that leaves no room for ambiguity, it tells exactly what the objective is in a clear and simple way. It also specifies the place, narrowing things. As a result of this purpose you are able to know to who is the action directed, what is going to be done, and where the action is taking place. The word "neighbors" refer to a specific population, making it accesible.
The other options are too general, by using "girls", "students", "consumers", a great number of possibilities could be considered.