a) One thousandth part of the upper portion of the hair point in size
b) One hundred-thousandth part of the upper portion of the hair point in size
c) One ten-thousandth part of the upper portion of the hair point in size
d) One thousand-thousandth part of the upper portion of the hair point in size
The correct answer is
c) One ten-thousandth part of the upper portion of the hair point in size