Final answer:
The correct answer is d. both b & c. A thermometer should be calibrated if it has been dropped and after an extreme temperature change.
Step-by-step explanation:
The correct answer is d. both b & c. A thermometer should be calibrated if it has been dropped and after an extreme temperature change. Calibrating the thermometer ensures that it is accurate and provides precise temperature measurements. It is important to calibrate the thermometer after it has been dropped to ensure that the impact did not affect its accuracy, and after an extreme temperature change to ensure that the calibration is adjusted to the new temperature range.