Final answer:
The word "vestige" is best matched with the word "trace", which signifies a remaining piece or indication of something that is no longer present.
Step-by-step explanation:
The word "vestige" refers to a trace, mark, or visible sign left by something that is now lost or vanished. So, when considering the provided options, the word that matches the closest in meaning to "vestige" is "trace" (a).
Looking at other similar questions, the word that is closest to the same meaning as hypothesis would be "suggestion" (d), as a hypothesis is a tentative explanation that requires further investigation. The word "theory" in the context of the theory of evolution suggests a well-substantiated explanation based on evidence, so "hypothesis" (b) might be a less developed stage before a theory. In psychology, the "engram" (a) is the term used to describe a physical trace of memory.
Vestigial structures, mentioned in biology, are physical remnants of organs or structures that had a function in an early ancestor but are currently of little or no use to the organism. This indicates a shared evolutionary history.