Hi! The answer would be B. pollution from a factory entering a river because humans built the factory so that it would drain into the river, therefore it is unnatural.
I estimate about 1-2 Hours. I am not an expert but I would guess that for a chocolate to melt in a room temperature it would probably take that time.
The answer is "bb" because a gene must have alleles that are both recessive in order for the recessive trsit to take over.
