language

Answer: words

Words are the basic units of language. They carry meaning and can be combined according to grammatical rules to form phrases and sentences.

Why the other choices are incorrect:

• tongue: This usually refers to the physical organ or informally to a native language; the physical tongue is not required for language because sign languages and other modalities convey language without it.

• slang: Slang is an optional, informal subset of vocabulary used in certain groups or contexts; it is not essential for a language to exist.

• writing: Writing is a way to record language but is not required for a language to exist, since many languages are only spoken and have no writing system.

Key idea: A language needs meaningful units (like words) and rules to combine them; other things such as slang, writing, or the physical tongue are not universally required.