B

The visible spectrum for humans ranges from approximately 380 nm (nanometers) to 750 nm. To find the number of wavelengths, we need to calculate the number of wavelengths within this range.

• The lower end of the visible spectrum is 380 nm.
• The upper end is 750 nm.
• The range of wavelengths = 750 nm - 380 nm = 370 nm.

Since the question is asking for the number of distinct wavelengths, we usually consider the range of visible light which can roughly correspond to around 6000 different shades or colors in the spectrum that humans can perceive.
Therefore, the best answer is approximately 6000 distinct wavelengths in the visible spectrum.