The correct option is: a. Short reads could have come from anywhere in the repeated region, so you can't build overlaps
Repetitive regions in the genome, such as the telomeric repeat sequence you mentioned (5'-TTAGGG-3'), pose challenges for genome sequence assembly from short reads. In repetitive regions, short reads could match to multiple locations within the repeat units, and it becomes difficult to determine the correct order and arrangement of these reads.
This ambiguity makes it challenging to build overlaps and assemble the short reads into a continuous and accurate representation of the entire genome. As a result, assembling genomes with repetitive regions using only short reads can lead to gaps, misassemblies, or other errors in the final genome assembly.