If altitude bubble is provided both on index frame as well as on telescope of a theodolite, then the instrument is levelled with reference to_________________?_x005F_x000D_1. altitude bubble on index frame_x005F_x000D_2. altitude bubble on index frame if it is to be used as a level_x005F_x000D_3. altitude bubble on telescope_x005F_x000D_4. altitude bubble on telescope if it is to be used as a level_x005F_x000D_The correct answer is?

• A. only (1)
• B. both (1) and (4)
• C. only (3)
• D. both (2) and (3)