A clinical thermometer reads temperature from
(A) $ 35^\circ C $ to $ 42^\circ C $
(B) $ 0^\circ C $ to $ 100^\circ C $
(C) $ 25^\circ C $ to $ 42^\circ C $
(D) $ 35^\circ C $ to $ 62^\circ C $

Hint The clinical thermometer is specifically designed to read temperatures achievable by a living human body. The human body has a very short range variation of temperature.

Complete step by step answer
In general, thermometers are instruments designed to read the temperature of an object. Different thermometers are designed with different principles each having its own level of accuracy and resolution. Each of these thermometers has its specific purpose, and situations where they are optimized to be used. When a thermometer is based on usage and only detects a specific range of temperature, it will be inefficient to calibrate such a thermometer to read other far beyond or far below this range of temperature.
The clinical thermometer, specifically, is a type of thermometer which is designed to detect and read the range of temperatures that can be achieved by the living human body. It is mainly utilized to detect fever which is the increase in body temperature of the body, or hypothermia which is characterized as a decrease in the temperature of the body. The temperature of the normal human body is agreed to be about $ 37^\circ C $ , any temperature above a maximum of $ 38^\circ C $ is considered fever and a temperature below, and a body temperature around $ 35^\circ C $ is considered hypothermia.
Based on these, it is safe to conclude that a clinical thermometer which reads from anything as low as $ 25^\circ C $ and up to then $ 62^\circ C $ would be considered inefficient.
Hence the clinical temperature must be $ 35^\circ C - 42^\circ C $ .
Thus the correct option is A.

Note
The inefficiency of the thermometer as we mean is the extra inaccuracy it’ll possess due to the unnecessary range. For example, if a mercury in glass thermometer that is to be used as a clinical thermometer is marked from say, $ 0^\circ C - 100^\circ C $ , the resolution of the thermometer will be low thus the accuracy will be low compared to the same thermometer if it has been marked from $ 35^\circ C - 42^\circ C $ .