There are several. there is rainwater*, glaciers, and rivers/streams.
*the rainwater I am talking about is the kind that falls from the country. no acid rain
Answer;
A) island forms and mainland forms descended from common ancestors.
Explanation;
-Islands tend to host very distinct but limited sets or species; on a given island a spectacular collection of one related group of species would be present and thriving, but many entire families or even higher taxa would be completely absent.
-All the species on the islands and the nearest continent are closely related to one another, however, each species had a set of adaptations that suits it for a particular environment. This means that the island forms and mainland forms descended from common ancestors.
Answer:
your answer is Choice C they would have 50% having the DMD. It is 100% correct I am taking biology classes and it is correct. And I also looked it up it is 50% I promise you there's no doubt 100%