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What is back-lash error and how it is avoided​

The correct answer is - it is an error in the observation.

Explanation:

Backlash error is the error in the motion that takes place during shifting the direction of gears. A backlash error is an error in the observation which occurs due to the wear and tear of threads of the screw observed that takes place at the time of reversing the direction of rotation of the thimble where the tip of the screw does not move in the opposite direction but remains stationary for a part of the rotation.

Avoid backlash error:

While taking measurements, the screw should be rotated in one direction only.

3.2x10^7

there is no correct list among the choices you've provided.

the list might look something like this:

-- baby human

-- piccolo

-- flute

-- soprano singer

-- trumpet

-- tenor singer

-- trombone

-- baritone singer

-- baritone horn

-- bass singer

-- tuba

since i had to make up the list myself, i made it easy on myself, and i didn't try to shuffle the string instruments and woodwinds into it too.