Which of the following is a reason for inverse relationship between insolation and cloud cover in sky?

• A. Sunshine duration records are caused by sun being obstructed by transparent cloud cover
• B. Sunshine duration records are caused by sun being obstructed by opaque cloud cover
• C. Sunshine duration records are caused by sunshine being transmitted through opaque cloud cover
• D. Sunshine duration records are caused by sun being obstructed by cloud cover