a) must be placed at a distance of 1m (1yd) from each end of the halfway line.
b) are positioned on the touch line at each end of the halfway line.
c) may be placed at a distance of 1m (1yd) from each end of the halfway line.
d) must be placed at a distance of at least 1.5m (1.5yd) from each end of the halfway line.