To determine the best temperature to heat the tea when adding sugar to make it as sweet as possible, we need to look at a solubility graph, which typically shows how the solubility of a substance (like sugar) changes with temperature.
In general, sugar's solubility increases with temperature; this means that at higher temperatures, more sugar can dissolve in the liquid. If the options provided are:
A. 55
B. 1414
C. 1616
D. 3939
From these options, the best choice for maximizing sugar solubility would be the highest temperature listed. Therefore, if we assume "39" refers to degrees Celsius (or another temperature scale), the best answer would be D. 3939, as it would allow the maximum solubility of sugar in the tea, leading to a sweeter beverage.
If the intended context suggests something different for the numerical values, typically, the highest temperature available on the graph range would be the ideal choice. Always refer to the specific solubility graph for confirmation.