**Core Concept**
The Snellen chart is a standardized visual acuity chart used to measure the sharpness of vision. It consists of lines of increasingly smaller letters, with each line representing a decrement in visual acuity. The distance at which a person can read the first topmost letter on the Snellen chart is an indicator of their visual acuity.

**Why the Correct Answer is Right**
The correct answer is related to the concept of visual acuity and the design of the Snellen chart. The chart is designed such that a person with normal vision can read the first topmost letter at a distance of 6 meters. This is because the chart is calibrated to have a certain number of letters per line, and the distance at which a person can read the first topmost letter is a reflection of their ability to resolve details at a given distance. In this case, the person is able to read the first topmost letter at 6/6, which means they can see objects clearly at a distance of 6 meters.

**Why Each Wrong Option is Incorrect**
* **Option A:** This option would be incorrect because it is not a standard distance at which a person with normal vision can read the first topmost letter on the Snellen chart.
* **Option B:** This option would be incorrect because it is not a standard distance at which a person with normal vision can read the first topmost letter on the Snellen chart.
* **Option D:** This option would be incorrect because it is not a standard distance at which a person with normal vision can read the first topmost letter on the Snellen chart.

**Clinical Pearl / High-Yield Fact**
It's essential to remember that visual acuity is a measure of the sharpness of vision, not the field of vision. A person can have normal visual acuity but still have impaired peripheral vision.

**Correct Answer:** C. 6 meters.