C, i think?? I hope it is right. ;)
What book is this? and if it isn't a book what is it?
The underlined phrase in the given sentence above is "during the tour". The word that is being modified by this phrase is option B. Bought. What did they do during the tour? They BOUGHT souvenirs. The word bought describes what they were doing during the tour.
Here are the letter names in order including the ones you have already written down:
B, A, D, G, E, C, F, F, G, E, D, A, B, F