Participles can be used as adverbs when they refer to the subject, and
tell some circumstance about the action, as "Walking along the street,
John saw your friend." "Walking along the street" tells the circumstance
under which the subject, John, saw your friend; therefore "walking" is
adverbial--"Promenante sur la strato, Johano vidis vian amikon." If it
were the friend who was walking, it must be "Johano vidis vian amikon,
promenantan sur la strato."
(Examine in this way the sentences in the following exercise).