The correct option is C Well
Discourse Markers are words or phrases used to
connect or manage the flow of written or oral conversations. These can be used at the start
or end of a sentence. ‘Well’, ‘However’, ‘So’, ‘Anyway’ are few examples of
discourse markers. In the given options for identifying the discourse markers, option A is 'I' which is a pronoun, option B and D are 'guess' and 'go' respectively which are verbs. So, the discourse marker in the sentence is 'well' which is option C and is the correct option.