圆x2+y2-2x+4y-4=0的圆心坐标是[ ]
A.(-2,4)
B.(2,-4)
C.(-1,2)
D.(1,-2)
答案:D
Mrs. Smith has ______ 8-year-old daughter who has won two national painting prizes.
A.a
B.an
C.the
D.不填
气动夯管锤的特点有( )。
A.地层适用范围广
B.铺管精度较高
C.对地表的影响较大
D.夯管锤铺管适合较长长度的管道铺设
E.投资和施工成本低