Answer:
D. 4ft by 10ft
Explanation:
Since each square represents 4 feet and the door is 2 blocks plus a bit up it can't be 8 ft since 8ft would only be 2 blocks exactly, this also rules out B since 12 ft would need to be 3 blocks high. this leaves A and D. The third square is only half of a normal square which means its half of 4, 2. You add this to 8 to get 10.