A square loop of side length $a$ is moving away from an infinitely long current carrying conductor at a constant speed $v$ as shown. Let $x$ be the instantaneous distance between the long conductor and side $A B$. The mutual inductance $M$ of the square loop-long conductor pair changes with time $t$ according to which of the following graphs?

• A

  
  
• B

  
  
• Correct answer
  C

  
  
• D

  
  

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