Step 1: Recall the definition of a noun.
A noun names a person, place, thing, or idea. The sentence is: "The rapid expansion of technology has transformed modern medical treatments."
Step 2: Identify each noun.
"Expansion" (abstract noun), "technology" (abstract noun), and "treatments" (noun) are the nouns.
Step 3: Eliminate non-nouns.
"Rapid" and "medical" are adjectives; "transformed" is a verb. Options (2), (3), and (4) include adjectives or verbs, making only option (1) correct.
\[ \boxed{\text{expansion, technology, treatments}} \]