Question

Why do we only know a little bit about Pluto?

Answer 1

Pluto is pretty far away from our planet, the Earth. It'd take a lot of years for the research and many years for the return.

So the answer is D.

For all other choices.

A is pretty wrong. As you should know that Pluto is VERY far from the Sun.

B is an assumption but not really that much logical.

For C, we know where Pluto is.

D is the most logical answer for the question as it is too far away for the research. After all It'd take more than approximately 10 years.