下列图形最有可能是哪段代码执行后的结果？（ ）
import turtle turtle.forward(100) turtle.left(90) turtle.circle(50,180) turtle.down()
import turtle turtle.forward(100) turtle.left(90) turtle.circle(50,-180) turtle.down()
import turtle turtle.forward(100) turtle.left(90) turtle.circle(50,90) turtle.down()
import turtle turtle.forward(100) turtle.left(90) turtle.circle(50,-90) turtle.down()
