Final answer:
The root word 'morph' can sometimes stand on its own, compared to the other options which are a prefix or suffixes that cannot stand alone. 'Morph' means 'shape' or 'form' and is a standalone word in specific contexts such as biology. (option B is the correct answer).
Step-by-step explanation:
The correct answer is The root word 'morph'. A root word is the primary lexical unit of a word, and morph, which means 'shape' or 'form', can stand alone as a word. The prefix 're-' and the suffix '-ing' cannot stand alone as they are bound morphemes that must be attached to other morphemes to convey meaning. The root word 'phon' typically does not stand alone in Modern English but is found in various words related to sound.
For example, 'morph' is used in biology to describe distinct forms within a species. In contrast, 'phon' would combine with other morphemes to create words like 'telephone' or 'microphone', whereas 're-' would be prepended to verbs to indicate repetition, as in 'renew' or 'restart', and '-ing' is a common suffix used to form gerunds or present participles, like 'running' or 'singing'.