Which one among the following is the major cause of blurring and unsharp images of objects observed through very large telescope at the extreme limit of magnification?

• A

  Air turbulence of earth's atmosphere
• B

  Poor optical polish achievable on large mirrors
• Correct answer
  C

  Poor tracking capacities of telescopes
• D

  Varying density of air in the Earth's atmosphere

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