. Which of the following is the most precise instrument for measuring length?
(a) vernier calipers having 20 divisions on the sliding scale which coincide with 19 divisions on the main millimeter scale
(b) a screw gauge having pitch 1 mm and 50 divisions on the circular scale
(c) a vernier scale of least count 0.01 mm
(d) a screw gauge of least count 0.001 mm