下列程序哪个是画一个三角形？（）
turtle.forward(100) turtle.left(120) turtle.forward(100) turtle.right(60) turtle.backward(100)
turtle.forward(100) turtle.left(60) turtle.forward(100) turtle.right(60) turtle.backward(100)
turtle.forward(100) turtle.left(120) turtle.forward(100) turtle.right(60) turtle.forward(100)
turtle.forward(100) turtle.left(120) turtle.forward(100) turtle.right(120) turtle.forward(100)
