圆x2+y2−2x−8y+13=0的圆心到直线ax+y−1=0的距离为1，则a=（）。
A.
B.
C.
D.2
参考答案：A
What _____ you _____ to do when you _____ high school? [ ]
A. do; want; finish
B. are; want; finish
C. are; going; are going to finish
D. are; want; are going to finish
含朱砂的中成药中含有
A．玫瑰花、款冬花、扁豆花、佛手片B．刺猬皮、九香虫C．黄精、党参、天冬D．杏仁、柏子仁、砂仁E．厚朴、肉桂、砂仁
