警官達は通りをパトロールしていた。

topic marker particle; indicates contrast with another option (stated or unstated); adds emphasis

avenue; street; way; road; coming and going; street traffic; flow (of water, air, etc.); transmission (of sound); reach (e.g. of voice); fame; reputation; popularity; the same status or way; as (e.g. as expected, as I said); understanding; comprehension; counter for sets of things; counter for methods, ways, types

indicates direct object of action; indicates subject of causative expression; indicates an area traversed; indicates time (period) over which action takes place; indicates point of departure or separation of action; indicates object of desire, like, hate, etc.

patrol