In heterogeneous mixtures there are distinguishable constituents, it means that we could have liquids and solids into the same mixture unlike homogeneous mixtures in which the constituents are indistinguishable (they are usually single-phased (of course, a pure solid or a pure liquid are often single-phased).
A pure solid and a pure liquid are definitely a single phase because they are so united, or homogeneous. This leads to a homogeneous mixture also being a single phase. The option that cannot be considered a single phase is D. a heterogeneous mixture.
The United States leads the world with over 260 billion short tons of recoverable coal reserves—28% of total global reserves and 50% more than Russia, which possesses the world's second largest reserves. so the answer would be 28%
