The author claims all of the following to be the benefits

Đáp án A
Các đáp án B, C, D đều được nhắc đến ở đoạn cuối:
In the summer, rooftop gardens prevent buildings from absorbing heat from the sun, which can significantly reduce cooling bills. In the winter, gardens help hold in the heat that materials like brick and concrete radiate so quickly, leading to savings on heating bills. Rooftop vegetable and herb gardens can also provide fresh food for city dwellersLike parks, rooftop gardens help to replace carbon dioxide in the air with nourishing oxygen.
Chỉ có A là không được nhắc đến