a)He believes it is stealthy and all-encompassing.
He describes the fog as being everywhere when he says its on the window-panes, in the drain pools, and "into the corners of the evening". All-encompassing means that it is everywhere, surrounding everything. The way the speaker leaves out any mention of sound or noise makes it seem as though this fog moves quietly. The description of the fog going to the window-panes, the corners, and the pools gives it a quick stealthy feel.
Okay, so I am confused about what you're asking here.
Knows little. 2 and 3 are both presuming too much, as it's the writer's duty to get them interested and informed. 4 basically doesn't matter, and furthermore may not even apply in many forms of writing. 1 is the best answer, as writing for general audiences is intended to inform and expand the horizons of the reader.
