锯割低碳钢、铸铁、铜、铝等宜选用（）锯条。
A.细齿
B.小齿
C.中齿
D.粗齿
参考答案：D
Between the two hills there _________ a deep river.
A．are
B．have
C．has
D．is
微生物根部定植 colonization of root by microorganism
