Answer:
(4) Water, stirring, and filtering
Explanation:
The added water will dissolve the sugar but not the sand. When you filter the mixture, the sand will be trapped in the filter paper and the dissolved sugar will pass through the pores of the paper.
(1) and (2) are wrong. You don't separate a mixture of sugar and sand by adding more sand. Furthermore, neither substance will boil at 100 °C.
(3) is wrong. You can dissolve the sugar in water but, if you boil the water away, the sugar and sand will still be together.
