Assertion : Sky wave signals are used for long distance radio communication. These signals are in general, less stable than ground wave signals. Reason : The state of ionosphere varies from hour to hour, day to day and season to season.

• Correct answer
  A

  If both assertion and reason are true and reason is the correct explanation of assertion.
• B

  If both assertion and reason are true but reason is not the correct explanation of assertion.
• C

  If assertion is true but reason is false.
• D

  If both assertion and reason are false.

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