A man wearing dark glasses taps his cane against the pavement. his German Shepherd leas him across an alley.

要準確地翻譯好這句話，首先得弄清楚以下幾個詞的意思：

dark glasses: glasses with dark glass in them that you wear to protect your eyes from the sun or to hide your eyes

tap: v. hit sb/sth quickly and lightly

tap sth (against/on sth): strike (sth) lightly with sth

cane: n. a long stick used especially by old, ill or blind people to help them walk

pavement: n. (Brit) (US sidewalk) path with a paved surface at the side of a road for people to walk on

shepherd: v. guide or direct (people) as if they were sheep; guide sb or a group of people somewhere, making sure they go where you want them to go

shepherd: n. A shepherd is a person, especially a man, whose job is to look after sheep or someone takes somebody somewhere to make sure that you arrive at the right place safely

German shepherd (or Alsatian): a large brown and black dog, often used for guarding buildings and in police work

alley: narrow passage, esp. between or behind houses or other buildings, usu. for pedestrians only; path bordered by trees or hedges in a garden or park

所以這句話的譯文是：一個帶著墨鏡的人倚著柺杖在人行道上走著，他的德國導盲犬領著他穿過小路（小巷；衚衕）。