A:ρ= 1sinθ+cosθ
B:ρ= 1sinθ-cosθ
C:θ= π4 (ρ∈R)
D:θ= 3π4 (ρ∈R)
____质地松软,吸水力强,适合于水墨书写、绘画和印刷用,如中国的宣纸。
( ) Let's put the magnet (磁铁)near the nails.