Simply put, a genetic mutation comes from a change in the DNA; this change can result from an extrachromosomal element, an alteration of the inherited nucleotide...
The basic building block of nucleic acids, such as DNA and RNA. It is an organic compound made up of nitrogenous, a sugar, and a phosphate group (http://www.biology-online.org/dictionary/Nucleotide)
It is called a watershed.
There are many fish in the world.
but it’s probably not that hard tbh.
For this item, I would go with letter "D. physical destruction of marine habitats". Many of the modern ways of fishing poses an irreversible destruction to marine habitats. These practices include trawling, lining methods, purse seining, etc.
