Answer:
Option B , 10-20%
Step-by-step explanation:
If we look at the map we could see that majority of the coastal area of the United States is moderately eroding. This color is denoted by orange. Hence, one thing is sure that moderately eroding coastline comprises of more than 50% of the total coast line.
Hence, option C cannot be correct.
Now if we just look at the red colored coast line we could see that a considerable length of red coast can be seen which is any case is definitely more than 5%. Hence, the only option left is option B.