Answer: Because of the fine bore of the tube.
Step-by-step explanation:
Temperature is the degree of hotness and coldness. And thermometer is the instrument use to measure temperature.
The two most common types of themometric fluids for thermometer are alcohol and mercury.
What makes a clinical thermometer suitable for measuring small changes in body temperature is because of the fine bore of the tube which makes it possible for small temperature changes to cause large changes in the length of mercury columns, making the thermometer very sensitive to temperature changes.
The most prominent feature of the thermometer is the kink or constriction of bore near the bulb.