Fraternal twins are the twins which are produced from the fertilization of two different eggs by two different sperms. These eggs are released at the same time.
So as fraternal twins are produced from fertilization of two different eggs therefore they share 50% of genes with each other just like other siblings. They are also called dizygotic twins
Identical twins are produce from a sigle fertilized cell which later divides into two cell mass. Indentical twins share 100% gene. Therefore the correct answer is 50%.
.B) You would place newborn curly-whiskered mud rats with bald mud rat parents and place newborn bald mud rats with curly-whiskered mud rat parents. Finally, let some mud rats of both species be raised by their own species. Then you would compare the outcomes.