import turtle


def draw_square(pen, size, color="black", fill=None):
    """Draw a square with optional fill color."""
    pen.color(color)
    if fill:
        pen.fillcolor(fill)
        pen.begin_fill()
    for _ in range(4):
        pen.forward(size)
        pen.right(90)
    if fill:
        pen.end_fill()

def draw_rectangle(pen, width, height, color="black", fill=None):
    """Draw a rectangle with optional fill color."""
    pen.color(color)
    if fill:
        pen.fillcolor(fill)
        pen.begin_fill()
    for _ in range(2):
        pen.forward(width)
        pen.right(90)
        pen.forward(height)
        pen.right(90)
    if fill:
        pen.end_fill()

def draw_triangle(pen, size, color="black", fill=None):
    """Draw an equilateral triangle with optional fill color."""
    pen.color(color)
    if fill:
        pen.fillcolor(fill)
        pen.begin_fill()
    for _ in range(3):
        pen.forward(size)
        pen.left(120)
    if fill:
        pen.end_fill()

def draw_circle(pen, radius, color="black", fill=None):
    """Draw a circle with optional fill color."""
    pen.color(color)
    if fill:
        pen.fillcolor(fill)
        pen.begin_fill()
    pen.circle(radius)
    if fill:
        pen.end_fill()