(N/A) The process of transcription in eukaryotes is complex and involves the following steps:
$(i)$ There are three types of $RNA$ polymerases in the nucleus. $RNA$ polymerase $I$ transcribes $r-RNA$ ($28S, 18S$,and $5.8S$). $RNA$ polymerase $III$ is responsible for the transcription of $t-RNA$,$5S$ $r-RNA$,and $sn-RNAs$ (small nuclear $RNAs$). $RNA$ polymerase $II$ transcribes the precursor of $m-RNA$,which is called heterogeneous nuclear $RNA$ $(hn-RNA)$.
(ii) The primary transcript contains both exons and introns and is non-functional. It undergoes a process called splicing,where introns are removed and exons are joined in a defined order. The $hn-RNA$ also undergoes capping and tailing. In capping,an unusual nucleotide,methyl guanosine triphosphate,is added to the $5'$ end of the $hn-RNA$. In tailing,an adenylate residue $(200-300)$ is added at the $3'$ end in a template-independent manner.
(iii) The fully processed $hn-RNA$,now called $m-RNA$,is transported out of the nucleus for translation.