答案

When advanced economic development has tremendously raised the living standard, what the public are concerned about has been beyond the material life. On the contrary, social welfare, such as public facilities, attracts people more. In the debate over the national investment on public parks or a sport field, I vote for the former. 
To begin with, it is a construction benefiting the majority of the public. Different from a sport field for physical exercises, the majority of whose participants are the youth, active and energetic, a public park is where everyone can visit. When the expenditure the government has got cannot meet the both needs of public parks and a sport field, the choice that meets the desire of the majority is where the money should go, for equity and fairness in the society. 
Moreover, people have a place to get themselves relaxed after a busy day. A public park provides people with a great variety of choices. For example, the elderly can get themselves exercised in the morning; the young finally find themselves a place for dating; the families can have a picnic on the lawn. 
Furthermore, it contributes to the natural environment in the city. City is a place where tall buildings, heavy traffic, and industrial pollution have occupied most of the space. When carbon dioxide has caused serious environment problems, such as global warming, what the public need is oxygen, the source of which is green plants. A public park, undoubtedly, will be planted with a great amount of green plants, purifying the air and adding vitality to the environment. There is no doubt that parks in the city centre are considered as “lung of the city”. 
To end up, as an option benefiting the majority, as well as bringing people a place for relaxing, investment on the public parks, which makes great contributions to the natural environment, is a better choice in contrast to a sport field.