Answer:
The answer is absolute threshold.
Step-by-step explanation:
The absolute threshold is described as the lowest limit our senses can perceive. For example, auditory sensiblity can be measured by gradually increasing a sound frequency. The person tested must then determine at what point he starts hearing the frequency.
In the example, the olfatory threshold of Leronardo is lower (more sensible) than his grandparents'. This makes sense, as most of our sensorial thresholds tend to diminish as we get older.