The correct answer is D. All of the above.
The maximum longitudinal grade of a taxiway is 3%, which means that for every 100 feet of taxiway, the elevation should change by 3 feet. The permissible rate of change of grade is 1%, which means that the grade of the taxiway should not change more than 1% in any 100 feet. The permissible transverse grade of a taxiway is 1.5%, which means that the side-to-side slope of the taxiway should not exceed 1.5%.
These requirements are in place to ensure that aircraft can taxi safely and efficiently on the taxiway. The maximum longitudinal grade is limited to 3% to prevent aircraft from rolling backwards when they are stopped on a slope. The permissible rate of change of grade is limited to 1% to prevent aircraft from becoming unstable while taxiing. The permissible transverse grade is limited to 1.5% to prevent aircraft from tipping over while taxiing.