Many trees along the streets every year. So the air is very fresh now.A. plantB. are plan

问题补充：

Many trees along the streets every year. So the air is very fresh now.

A. plant

B. are planted

C. planted

D. were planted

答案：

A. plant

(答案→)B. are planted

C. planted

D. were planted

解析：句意：每年沿着大街都要种很多树。因此现在空气很清新。结合语境可知前文描述的是客观性的动作，故用一般现在时态。主语是动作对象，故用被动语态。选B。