Final answer:
The LD50 is the unit of measurement used to describe the effect of biological agents in terms of toxicity. The rad and gray are units used to measure the effects of nuclear radiation on biological tissue. So, the correct answer is D. LD50.
Step-by-step explanation:
The LD50 is the unit of measurement used to describe the effect of biological agents in terms of toxicity. The LD50 (lethal dose 50) represents the dose required to kill half the members of a tested population after a specified test duration. It is expressed in terms of weight of substance (milligrams) per unit weight of test animal (kilogram). The values for LD50 are typically determined through experiments using laboratory animals such as rats or mice.
On the other hand, to describe the effect of nuclear radiation on biological tissue, we use a unit called the rad. This is a measure of the amount of ionizing radiation energy absorbed by a mass of tissue and is defined as 0.01 joules of energy absorbed per kilogram of tissue (0.01 J/kg). The gray (Gy), which is the SI equivalent of the rad, also measures the effects of radiation on biological tissue, and is defined as 1 joule of radiation energy absorbed per kilogram of tissue (1 Gy = 1 J/kg).
Thus, the correct answer is D. LD50.