Gary went hiking he took along trail mix of nuts, raisins and other dried fruit. When he got home, he separated the raisins from the leftover mix...

As the name suggests, trail mix is a mixture. In fact, trail mix is a heterogeneous mixture, since all the components are distinguishable from each other and can be separated out easily. A mixture is characterized by the fact that each individual component retains their own property. In comparison, constituents of a compound lose their individual properties. This the reason Gary can separate out the raisins, by simply picking them out. This also means that Gary can pick out each individual nut or raisin, etc. and enjoy the taste of each one of them separately. Thus, the properties of raisins will remain the same and hence option D is correct. If the separated out raisins tasted different of were of smaller size or had a different color; it would have meant that trail mix is a compound (which is not the case). Hence, option D is correct.

Hope this helps.