Concept:The extract reveals the time of day through descriptions of heat, light, and atmospheric effects.
Explanation:The intense heat is clear from sweat collecting in Grooby's eyebrows.
The phrase "the air was actually burning gas" emphasises extreme midday temperature.
A haze makes the tractor appear to melt and dwindle, a typical shimmering effect of strong sunlight.
No signs of sunrise, sunset, darkness, or coolness appear in the extract.
These details all point to the hottest part of the day.
Answer:B. midday