If $a=3, b=5, c=7$ are the sides of a triangle ABC, then its circumradius is

• Correct answer
  A

  $\frac{7}{\sqrt{3}}$
• B

  $\frac{15}{2}$
• C

  $\frac{15 \sqrt{3}}{4}$
• D

  $\frac{\sqrt{3}}{2}$

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