The number of horizontal cross wires in a stadia diaphragm is

Answer: Option C

A stadia diaphragm is a special part of a surveying instrument (like a theodolite or level).
Its main purpose is to help determine distances.
The diaphragm has horizontal cross wires.
Typically, a stadia diaphragm contains three horizontal cross wires: one at the top, one in the middle (the central crosshair), and one at the bottom.
These wires are used to read the stadia intercept on a graduated staff held at a distance, which then helps calculate the distance.
Options A, B, and D are incorrect because stadia diaphragms are designed with three horizontal cross wires.