Original size: 10 kB
Order of restriction sites: X/B/X/B. Hence the correct option is e.
The original size of the linear DNA sample undergoing digestion by XhoI (Panel X), BamHI/XhoI (Panel B/X), and BamHI (Panel B) is 10 kilobases (10 kB). The order of the restriction sites in the linear DNA sequence corresponds to the arrangement described as X/B/X/B. This indicates that the XhoI recognition site (X) is followed by the BamHI recognition site (B), and then another XhoI site, and finally a BamHI site.
This order represents the specific locations where the DNA is cleaved by the respective restriction enzymes in the given panels: XhoI, BamHI/XhoI, and BamHI. Each slash (/) denotes a cleavage site in the sequence. Hence the correct option is e.