Answer: A) a device for measuring time.
Explanation: a word root is the most basic part of a word (without any prefixes or suffixes). From the given options, the one that represents the meaning of the word chronometer (according to the list of word roots), is the corresponding to option A: a device for measuring time, because "chronometer" is formed by two word roots: "chron" that means time and "meter" that means measure.
