The local police said they had received reports of seven cases of murder, which caused_____ among the

locals.[ ]

A. panic              

B. dilemma          

C. settlement          

D. coincidence

过去，美国中央大平原上发生“黑色风暴”的原因是  [ ]

A．风力过大    

B．气候干旱  

C．大量破坏了地表植被，黑土被风扬起       

D．工业区烟囱冒的黑烟