Read the article below and answer the question that follows.
Science Mysteries: How Many Species Are There?
You might think that after 200 years, the scientists who find, name, and describe Earth's species would be close to finished. But taxonomists, as organized as they may be, have no idea how many species Earth has. Nor can they even provide an educated guess. Although reporting over 16,000 new species every year, taxonomists still cannot predict how many more are undiscovered.
In total, taxonomists have categorized and listed 1.2 million species on Earth. At this point, you would think scientists should be able to use the information they have gathered to make good predictions about how many species an ecosystem can support. This would help them make better predictions about how many species are left to identify. So far, however, the guesses seem to vary so greatly that it seems there is no good theory for making a prediction.
One of the main problems is that most of the places that seem to have a lot of diverse species are in places that are hard to get to. One such place is the ocean, where scientists believe some 80 percent of Earth's creatures are hiding at depths too deep for us to study. In addition, many of the planet's most diverse areas are in remote places with few taxonomists.
Despite all the unknowns, scientists have agreed that there are between five and 15 million species left to discover on Earth. This is a huge range, but whether it's five or 15, taxonomists clearly still have a lot of work to do. And who knows, there may yet be a dragon or a Loch Ness monster left to discover.
Which of the following best paraphrases the paragraph in bold?
a It's hard to figure out how many species there are on the planet.
b Scientists are having a hard time figuring out how many species there are on Earth even though they know about 1.2 million of them.
c Scientists have labeled over one million species on this planet. They could use this information to make predictions about how many other species there are, but they can't agree on a theory.
d There are a lot of ways scientists can figure out how many species there are.