a) After having the meal, she went shopping.
b) On being told the party was cancelled, the girl burst into tears.
c) While walking along the street, Sandy answered.
Please, advise whether the ing-forms placed after prepositions act as Participle or Gerund.
I have always thought that it is gerund that comes after prepositions, but working on a grammar exercise that is devoted to participles, I felt doubt.