Classification (lexical category – predominant use): Three words are primarily common nouns in everyday use; one is frequently used as a verb as well as a noun. Identify the odd one out.

Introduction / Context:
Word-class classification can hinge on predominant grammatical use. “Teeth,” “sheep,” and “greed” function primarily as common nouns in neutral contexts (teeth = plural noun; sheep = plural-invariant noun; greed = abstract noun). “Sleep,” however, freely functions both as a noun (get some sleep) and as a verb (I sleep early). Reasoning tests often treat a flexible part-of-speech item as the odd one against items with predominantly nominal usage.

Given Data / Assumptions:

• TEETH → common plural noun; not typically a verb.
• SHEEP → common noun; plural-invariant; not a verb in standard usage.
• GREED → abstract noun; not a verb.
• SLEEP → can be both a common noun and a verb in everyday usage.

Concept / Approach:
Identify which word exhibits dual major category behavior (noun and verb) in general English usage. With three items strictly nominal and one flexibly nominal/verbal, the latter is the outlier. This retains objectivity and avoids subtle semantic debates about countability or irregular plurals.

Step-by-Step Solution:

Verification / Alternative check:
Substitute in frames: “to ____” works naturally for sleep; “to teeth/sheep/greed” does not function as standard English without specialized contexts.

Why Other Options Are Wrong:

Common Pitfalls:
Overanalyzing morphological quirks (sheep’s invariant plural) instead of focusing on part-of-speech flexibility.

Final Answer:
SLEEP