To determine which of the given numbers could represent the measure of an angle that is less than 180 degrees, we should examine each option individually:
- 120 degrees: This value is less than 180 degrees, thus it is a valid measure for an angle.
- 140 degrees: Similarly, this measure is also less than 180 degrees, making it another valid angle.
- 510 degrees: An angle of 510 degrees exceeds 180 degrees, therefore it cannot be considered a valid measure of an angle below 180 degrees.
In summary, the angles that could measure below 180 degrees are 120 degrees and 140 degrees. The option 510 degrees does not qualify as it exceeds the specified limit.