—Are you from Germany?
— _________.
A:Yes, I am
B:No, I am
C:Yes, I'm not
D:No, he isn't
小刚同学要用A4纸(长约30cm,宽约21cm)绘制校园操场(有周长400米的标准跑道)示意图,他选取的最适合的比例尺是( )