Explain (in one or two lines) the function of the following:
$(a)$ Promoter
$(b)$ $tRNA$
$(c)$ Exons

(N/A) Promoter: $A$ promoter is a region of $DNA$ that initiates the process of transcription by serving as the binding site for $RNA$ polymerase.
$(b)$ $tRNA$: $tRNA$ (transfer $RNA$) reads the genetic code on $mRNA$ and carries specific amino acids to the ribosome during protein synthesis.
$(c)$ Exons: Exons are the coding sequences of $DNA$ in eukaryotes that are transcribed into $mRNA$ and translated into proteins.