Corrections for curvature and refraction (c r) are applied to: . a. benchmark elevations (BM)
b. both foresight rod readings (FS) and backsight rod readings (BS)
c. foresight rod readings (FS)
d. backsight rod readings (BS)

b.

Explanation:

Foresight rod reading is any measurement taken at a given sight to determine a particular elevation. The backsight rod readings are usually used to a point of certain elevation. It is added to the elevation to determine the height of the instrument. These are phenomena are used in differential leveling and are applied to corrections for curvature and refraction.

import math

x=int(input("enter a number: "))

print (math.sqrt(math.fabs(

answer:

explain:

we don't have any choices.