Final answer:
Thermometers, except for bimetallic types, should generally be calibrated annually or as recommended by the manufacturer, although more frequent calibration might be needed in cases where precision is crucial (D).
Step-by-step explanation:
Most thermometers, with the exception of bimetallic ones, should typically be calibrated either annually or according to the manufacturer's recommendations. However, the frequency of calibration can also depend on how often the thermometer is used, the conditions in which it is used, and the precision required for the temperature measurements.
For critical measurements where precision is paramount, more frequent calibrations such as monthly or even weekly may be necessary. When used in a classroom setting for educational purposes, annual calibration might be sufficient unless the instrument is frequently used or subjected to conditions that might cause it to drift from its calibrated state.