下列树种，不适合用作地被的是（）。
A.常春藤
B.杜鹃
C.梧桐
D.八角金盘
参考答案：C
Mary is very late, she ______.
A．may miss her train
B．may have missed her train
C．must miss her train
D．could miss her train
锪钻用于加工（）。
A.盲孔
B.锥孔
C.阶梯孔
D.通孔
