A heterogeneous mixture composes of non- uniform components, so the concrete would be the answer, because you can tell the components from one another.
I'm pretty sure the answer is D
The answer is stem cells, they consist of classes of cells
that are undifferentiated and are able to be classified them into types like
specialized cells. They consist of having two main sources that will help them
develop and mature, these main sources are called the embryonic stem cell and
the adult stem cell.