Which of the following is the most precise measurement?

Which of the following is the most precise instrument for measuring length?

Which of the following is the most precise instrument for measuring length?

Which of the following is the most precise instrument for measuring length?

Which of the following is the most accurate measurement?

Which of the following is the most accurate measurement?

Which of the following is the most precise devise for measuring length ? (a) a Vernier callipers with 20 divisions on the sliding scals, coindiing with 19 main scale divions (b) a screw gauge of pitch 1mm and 100 divisions on the circular scale (c ) an optical instrument that can measure length to within a wave length of light.