The depth of an arch is the distance between A. Ground level and springing line B. Crown and springing line C. Crown and ground level D. Intrados and extrados

The correct answer is: B. Crown and springing line.

The depth of an arch is the distance between the crown and the springing line. The crown is the highest point of the arch, and the springing line is the point where the arch meets the ground. The depth of an arch is important because it determines the amount of weight that the arch can support. A deeper arch can support more weight than a shallower arch.

The other options are incorrect because they do not measure the depth of the arch. Ground level is the level of the ground, and the intrados and extrados are the inner and outer surfaces of the arch, respectively.