Two different DNA samples were isolated from biological specimens. Further experiments demonstrated that one of these (X) was composed of $30 \% \mathrm{~A}, 30 \% \mathrm{G}, 20 \% \mathrm{~T}$ and $20 \%$ C but could not be cut by an exonuclease (an enzyme that cuts nucleotides from the ends of DNA). The second DNA sample (Y) could be cut by the exonuclease and was found to be composed of $30 \% \mathrm{~A}, 30 \% \mathrm{~T}, 20 \% \mathrm{G}$ and $20 \% \mathrm{C}$. Which of the following statements can be correctly deduced from the above?

• A

  DNA X has a double-stranded, linear structure.
• Correct answer
  B

  DNA X has a single-stranded, circular structure.
• C

  DNA Y has a double-stranded, circular structure.
• D

  DNA Y has a single-stranded, linear structure.

Hence, the correct answer is option: 'B'.