Final answer:
The amount of sand in an hourglass is variable and depends on the size of the hourglass, similar to how the weight of other items must be individually measured.
Step-by-step explanation:
The amount of sand in an hourglass can vary greatly. The correct answer to the question 'How many grams of sand is in an hourglass?' is A) Variable, depending on size. Like the weight of a bag of sand, the amount of sand in an hourglass must be measured for each specific hourglass as the size and volume can differ. Just as with determining the number of grams in your weight or the weight of a backpack, there is a degree of uncertainty and individual variation that requires measurement.