To solve this question, the user needs to know the definition of the speed of light.

The speed of light is defined as the distance light travels in a vacuum per unit of time.

Now, let's go through each option and explain why it is right or wrong:

A. 300,000 Mt/Sec: This option is incorrect because "Mt" is not a standard unit of measurement for speed. Also, the correct value of the speed of light is 299,792.458 km/s, which is not equal to 300,000 Mt/Sec.

B. 30000 Km/Sec: This option is incorrect because the actual value of the speed of light is much greater than 30,000 km/s. The correct value is around 299,792.458 km/s.

C. 300,000 Km/Sec: This option is correct. The speed of light in a vacuum is approximately 299,792.458 km/s, which is rounded up to 300,000 km/s for convenience.

D. None of the above: This option is incorrect because Option C is the correct answer.

Therefore, the Answer is: C. 300,000 Km/Sec