Clinical thermometers are examples of mercury-in-glass thermometers. They consist of a thin, sealed glass tube that is filled with mercury. The glass tube has a narrow constriction in it, which prevents the mercury from flowing back down the tube once it has expanded due to a rise in temperature.
When the thermometer is placed under the tongue or in the armpit, the heat from the body causes the mercury to expand and rise up the tube. The temperature can be read off a calibrated scale on the glass tube, which indicates the temperature based on the height of the mercury column.
Mercury-in-glass thermometers are commonly used in clinical settings because they are accurate and have a fast response time. The mercury expands and contracts rapidly in response to temperature changes, allowing for quick and accurate temperature readings.
Therefore, the correct answer is option (D) mercury-in-glass thermometer.