Step 1: Recall definitions.
Phonemes $=$ smallest units of sound; Morphemes $=$ smallest meaning-bearing units; Syntax $=$ rules for arranging words into sentences; Pragmatics $=$ use of language in context—social norms like politeness, turn-taking, implicature, deixis.
Step 2: Match to prompt.
The question asks about the {practical/social} side of communication $\Rightarrow$ how meaning changes with speaker, listener, setting, and intentions $\Rightarrow$ \fbox{Pragmatics}.