Question

The most accurate measurement of the lengths of long survey lines is made by using ?A. steel band B. invar tape C. electronic distance measuring equipment D. autoreduction tachometer

Answer 1

Electronic distance measuring equipment ... the most accuracy. 

there are also laser emitting devices which measure distances.  They are also accurate.

EDM emits electromagnetic waves, which are reflected by the objects at large distances.  Reflected signal is received and the phase shift between the two is calculated.   The  accuracy is  around 10⁻⁵ ..  1 mm in 100 meters  or more.