Which of the following best illustrates the concept of valid measurement?

The concept of valid measurement refers to the degree to which a tool accurately measures what it is intended to measure. In this case, a thermometer measuring temperature precisely exemplifies this principle because it correctly captures the temperature without bias or distortion. A precise thermometer provides reliable data that reflects true temperature values, thereby ensuring that the results can be trusted and used effectively.

Other options illustrate various forms of invalid measurement. For instance, a ruler that changes its length would yield inaccurate measurements due to its lack of consistency, making it unreliable for determining true lengths. Similarly, a survey that collects data on irrelevant factors does not measure the intended subject effectively, resulting in data that cannot be applied appropriately to the research. Lastly, a clock that is consistently fast provides a measurement of time, but it does so incorrectly, leading to systematic errors in timekeeping. Hence, the thermometer is the only example that fulfills the requirement of valid measurement by offering precise and accurate results.