Derivational morphemes are described as:

• A. Beginning of a word (prefixes such as pre, anti, sub) forming noun–verb pairs and compounds.
• B. Endings of a word that mark tense.
• C. External signs used in conversation.
• D. Syllable-level signs used for emphasis.

Answer: (A)

Derivational morphemes add or derive new words by attaching affixes to a base, often changing its meaning or its part of speech. Prefixes at the beginning of a word are a key way this happens. When you add prefixes like pre-, anti-, or sub- to a base, you create new words or related terms and can form compounds, such as preview, antibody, or subway. This contrasts with endings that mark tense, which are inflectional morphemes that modify a word’s time or form without creating a new word or changing its category. The other options describe signs or signals used in communication rather than process of word formation, so they don’t capture how derivational morphemes work.