Concept:Surveying instruments are designed for specific tasks. Measuring both horizontal and vertical angles requires an angle-measuring device.
Explanation:The theodolite is the standard field instrument that accurately measures both horizontal and vertical angles.
It has a telescope that rotates in both planes, allowing a surveyor to read angles precisely.
The prismatic compass is used mainly for measuring bearings and directions, not vertical angles.
The offset staff is used for measuring short distances or offsets during chain surveying.
The arrow is a marking pin used to mark stations or chain positions, and it does not measure any angle.
Therefore, only the theodolite fulfills the requirement of measuring both horizontal and vertical angles on the field.
Answer:A. theodolite