Which best explains why it is difficult to classify protists?
a they are all so much like one another.
b there is a lot of diversity between the organisms.
c they do not have anything in common with other organisms.
d they have structures that are hard to observe.

The best answer would be option - B.  

Explanation:

Protists are the group of organisms that are single-celled eukaryotes that are difficult to the classified. Protists are eukaryotes that do not belong to the plants, animals or fungi group.

Protists show more resemblance to the other group of organisms than other members of the protists. Due to this these organisms are difficult to classify and placed on the basis of conveniences like invertebrates and algae.

Thus, the correct answer would be option - B.

burning of wood and coal

explanation:

the panel also concluded there's a better than 95 percent probability that human-produced greenhouse gases such as carbon dioxide, methane and nitrous oxide have caused much of the observed increase in earth's temperatures over the past 50 years.