## Core Concept
The question pertains to the minimum illumination required for satisfactory vision, specifically in terms of foot-candles. Foot-candles are a unit of measurement for illuminance, which is the amount of light that falls on a surface. In the context of vision and lighting, understanding the required illuminance levels is crucial for ensuring that environments are adequately lit for various tasks.

## Why the Correct Answer is Right
The correct answer, , corresponds to a specific level of illumination that has been established as the minimum required for satisfactory vision in certain contexts. While the exact number can vary depending on the specific application (e.g., reading, surgery, or general ambient lighting), is a commonly cited threshold. This level ensures that there is sufficient light for the human eye to perceive details without causing discomfort or strain.

## Why Each Wrong Option is Incorrect
* **Option A:** - This option suggests a much lower level of illumination, which would likely be insufficient for tasks requiring detail perception, such as reading or watching a presentation.
* **Option B:** - Similarly, this option is also lower than the correct answer and might not provide adequate lighting for satisfactory vision in standard conditions.
* **Option D:** - This option suggests a higher level of illumination than necessary for minimum satisfactory vision, which, while not harmful, is more than the minimum required.

## Clinical Pearl / High-Yield Fact
A key point to remember is that the level of illumination can significantly affect visual performance and comfort. For general office work or reading, a commonly recommended level is around , but this can vary based on the task's specifics and the individual's visual acuity.

## Correct Answer: C. 10 Foot-candles.