Final answer:
A day would be less than 24 hours if the Earth was rotating faster, as a day is defined by one complete rotation of the Earth on its axis.
Thus (option A) is right answer.
Step-by-step explanation:
The question asks how long a day would be if the Earth were rotating faster than it currently does. If the Earth were rotating so fast that it completed one rotation in less than the usual 24 hours, then the length of a day would be less than 24 hours (Option A).
This is because one rotation of the Earth on its axis defines the length of one day. A regular solar day on Earth is about 24 hours, which is slightly longer than a sidereal day, the latter being the time it takes for the Earth to complete one rotation with respect to the distant stars.
The solar day is approximately 4 minutes longer because the Earth also moves along its orbit around the Sun, requiring an additional rotation of about 1/365 of a full turn to align again with the Sun.