—Do you plant trees in spring?

—Yes. Many trees ______ in our city every year. [ ]

A. are planting

B. are planted

C. were planted

D. be planted

宏观经济学中，表示失业率和工资增长率之间存在着负相关关系的曲线是( )。

A．洛伦茨曲线

B．菲利普斯曲线

C．拉弗曲线

D．瓦尔拉斯曲线