Final answer:
The approximate surface temperature of a B star is closest to 20,000 K, which is much higher than the surface temperature of the Sun, a G-type star.
Step-by-step explanation:
The approximate surface temperature of a B star is typically much higher than that of the Sun, which has a surface temperature of about 5800 K. Looking at the temperature range for different types of stars, we can determine that the surface temperature of a B star falls within the range of about 10,000 K to 30,000 K. Among the options provided, the closest approximation to the surface temperature of a B star would be D) 20,000 K.