**Core Concept**
The World Health Organization (WHO) defines blindness as a severe visual impairment that significantly affects a person's quality of life. This definition is used to establish global standards for vision impairment and blindness.

**Why the Correct Answer is Right**
The correct answer is based on the Snellen visual acuity chart, which is a widely used method to measure visual acuity. According to the Snellen chart, a person can be considered blind if they cannot count fingers at a distance of 3 meters (approximately 10 feet). This is because the Snellen chart measures visual acuity in terms of the distance at which a person can read a standard letter chart, with a normal visual acuity being 6/6 (6 meters). The Snellen chart is used as a reference to determine the severity of visual impairment.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because it does not specify a distance, making it an ambiguous choice.
**Option B:** This option is incorrect because it is too vague and does not provide a clear definition of blindness.
**Option C:** This option is incorrect because it does not match the WHO definition of blindness.

**Clinical Pearl / High-Yield Fact**
It's essential to remember that the definition of blindness can vary depending on the context and the organization providing the definition. However, the WHO definition is widely accepted and used as a global standard.

**Correct Answer:** . 20/200