Answer:
Density is nearly 3 cabs per hectare
Explanation:
Given -
There are three three intertidal regions.
Area of each intertidal region is
hectares.
Number of crab in the intertidal regions are as follows -
Intertidal region I - 7
Intertidal region I - 2
Intertidal region I - 6
Sum of crabs in all three regions is equal to

Total area of all three intertidal regions is equal to
hectares
Now density per hectare is equal to total population of crab divided by total area of all the three intertidal regions
Density 
Density is nearly 3 cabs per hectare
The answer is B. Uneven rock layer.
Uneven rock layer can directly lead to nonconformity on an exposed rock. Usually the rocks are layered evenly. When the rocks are uneven it will be exposed and show different kind of rocks.
I agree with the other person you answered the answer is B duckweed growth
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