Today in our environmental science lecture, we're discussing urban green spaces. A recent study in Melbourne tracked the effects of adding rooftop gardens to city buildings. The researchers measured temperature, air quality, and biodiversity over two years. They found that rooftop gardens reduced local temperatures by up to 3 degrees Celsius in summer, but only when the gardens covered at least 60% of the roof area. Additionally, bird species increased by 15% in areas within 500 meters of these gardens. However, the study noted that maintenance costs were higher than expected, mainly due to irrigation needs. The key takeaway is that green roofs require careful planning to maximize benefits.
❓ 关于屋顶花园的有效性，研究提出了什么建议？
A. A. 只有当覆盖的屋顶面积达到最低要求时，它们才能降低温度。
B. B. 无论花园大小，它们都能增加鸟类物种数量。
C. C. 由于维护需求低，它们具有成本效益。
D. D. 它们对空气质量没有影响。
✅ 正确答案
A. They reduce temperatures only if a minimum roof area is covered.