—Yeah. With the help of him, his sister writes as ________ as him.
A:care
B:careful
C:more carefully
D:carefully
在直角坐标系 xOy 中,圆 C1:(x−1)2+y2=1 ,圆 C2:(x−3)2+y2=9 ,以坐标原点 O 为极点,以 x 轴正半轴为极轴,建立极坐标系.
下列区域的划分以单一指标为依据的是( )①热量带 ②干湿区 ③我国三大自然区 ④文化区