Which of the following statements is/are true regarding the function of the spliceosome in heterogeneous nuclear RNA:
 
i. The spliceosome is responsible for removing introns from hnRNA and joining exons together to form mature mRNA.
ii. The spliceosome functions to add additional exons to hnRNA, increasing the length of the mRNA transcript.
iii. The spliceosome is involved in the transcription of hnRNA into mRNA within the cytoplasm.
iv. The spliceosome modifies hnRNA by converting exons into introns to prepare the transcript for translation.