Which of the following is the basis of the current standard for the meter?
The meter is defined in terms of the standard inch so that $2.54$ cm is exactly $1$ inch.
The meter is defined as the distance between precise scratch marks on a certain platinum-iridium bar that is kept under specified conditions.
The meter is defined as the distance that light travels in a specified time interval.
The meter is defined as a specified number of wavelengths of the orange-red light emitted by krypton-$86$.
The meter is defined as the length of a strand of carbon fiber that consists of a specified number of carbon-$12$ atoms.