Frontal resorption is caused due to:: (A) Light continuous force, (B) Heavy continuous force, (C) Heavy interrupted force, (D) Light interrupted force
Answer is A. Frontal resorption (direct/periosteal/forward resorption)

With light continuous forces, the bone is resorbed directly by a frontal osteoclastic attack. 
The first step in orthodontic tooth movement is the activation of osteoclasts.
In frontal resorption, resorption is initiated from the PDL side of the alveolar bone. It usually takes place after 2 days.