Final answer:
To produce 9 milligrams, you would need to measure in milligrams as it is the unit for mass. Conversion factors are used when changing from one unit of volume to another, but in this case, milligrams alone is the correct answer.
Step-by-step explanation:
To produce 9 milligrams of a substance, you would need to measure in milligrams for mass. If you were converting between units of volume, such as milliliters and liters, there are two conversion factors you might use. To convert liters to milliliters, you multiply by 1,000 since there are 1,000 milliliters in one liter. Conversely, when converting from milliliters to liters, you would divide by 1,000.
However, for direct conversion involving mass and not volume, milligrams will be used exclusively for the measurement required, as deciliters and liters are units of volume. Therefore, when considering the units from the list provided in the question, milligrams is the correct unit for measuring mass. Thus, the correct answer is simply the first option, which is milligrams. As the question does not pertain to volume but specifically asks for a mass measurement, milliliters, deciliters, and liters are not relevant in this context.