Why astronomers today are not able to say what the surface of Titan looks like?

This question is out of date. Until a couple of years ago the answer was d. The atmosphere is very murky and the surface is largely invisible through it. However, the Cini-Huygens mission used other methods to the cloud layer and image the surface from space, while also sending a small lander to the surface. Images of the surface of Titan are now abundant.