The correct answer is D. Both white and in the shade.
A white shelter reflects sunlight, which helps to keep the instrument cool. A shelter in the shade also helps to keep the instrument cool, as it is not directly exposed to the sun’s rays.
A black shelter would absorb sunlight, which would make the instrument warmer. A shelter in direct sunlight would also make the instrument warmer, as it would be directly exposed to the sun’s rays.
Therefore, the ideal shelter for housing a temperature-measurement instrument would be both white and in the shade.