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()