Final answer:
Long-terminal repeats are unique to viral-like retro elements, which are characterized by these repeats at the ends of their structure, unlike non-LTR retrotransposons like LINEs and SINEs.
Step-by-step explanation:
Long-terminal repeats (LTR) are unique to the group of transposons known as viral-like retro elements. LTR retrotransposons, similar to retroviruses, feature these repeating sequences at both ends of their structure. These sequences are used during the process of reverse transcription where DNA is synthesized from an RNA template. The presence of LTRs distinguishes them from non-LTR retrotransposons like Long Interspersed Nuclear Elements (LINEs) and Short Interspersed Nuclear Elements (SINEs), which lack long terminal repeats and instead have 5' and 3' untranslated regions (UTRs) flanking their open reading frames (ORFs) or non-genic DNA, respectively. LINEs are autonomous transposons which encode the enzymes necessary for transposition, whereas SINEs do not encode such enzymes and rely on the activity of LINEs for their mobility.
In summary, long-terminal repeats are a defining feature associated with viral-like retro elements specifically, making option c) Viral-like retro element the correct answer to the student's question.