The correct answer is C. throw of the switch.
The throw of the switch is the distance through which the tongue rail moves laterally at the toe of the switch for movement of trains. It is measured from the point where the tongue rail meets the stock rail to the point where it is parallel to the main line. The throw of the switch is important because it determines the amount of space that is available for trains to pass through the switch. If the throw of the switch is too small, trains may not be able to pass through the switch safely.
A flangeway clearance is the minimum distance between the flange of a wheel and the inside of the rail. It is important to ensure that there is enough flangeway clearance to prevent derailments.
Heel divergence is the difference in the elevation of the two rails at the toe of the switch. It is important to ensure that heel divergence is within the specified limits to prevent derailments.
None of the above options are correct.