Final answer:
The equivalent measure between the metric system and the apothecary system is C. 1 tsp = 5 mL, which is commonly used in medicine and cooking.
Step-by-step explanation:
The equivalent measure between the metric system and the apothecary system is C. 1 tsp = 5 mL. The apothecary system, which is historical and not frequently used in modern times, had various units such as the teaspoon (tsp), dram (dr), and grain (gr). The metric system, on the other hand, uses milliliters (mL) among other units to measure volume. To accurately convert from one system to the other, one must use appropriate conversion factors. For instance, the given conversion of 1 teaspoon to 5 milliliters is a standard equivalence in medicine for liquid medications and is also adopted in culinary measurements.