Which of these factors dependent on the vehicle driver has a significant influence on the driver's vision?

The question is about factors that depend on the driver and affect the sharpness of his vision. These are concentration, current well-being and health - answer C. Air temperature and humidity (A) and the condition of the roadway and the time of day (B) affect driving conditions, but do not depend on the driver.

Sharpness of vision is the ability to see details - to read a sign, to notice a pedestrian in dark clothes, to judge the distance to the car in front. It depends not only on the eyes, but on the state of the whole body: tiredness and lack of sleep lengthen the time the eye needs to focus and delay your reaction; illness, fever, headache, alcohol and some medicines make vision worse; being distracted by a phone means that you look at the road but do not see what is happening on it. The Road Traffic Act prohibits driving after drinking alcohol or taking substances with a similar effect, and requires every road user to be careful and to avoid actions that could endanger safety - driving when you cannot see clearly is such an action. Before a longer trip get enough sleep, when taking medicines check the leaflet, and when your eyes start to sting, take a break.

Legal basis: Art. 3 para. 1 and Art. 45 para. 1 point 1 of the Road Traffic Act (Prawo o ruchu drogowym)