19.
Your Answer is
Correct Answer is A
Explanation
A is correct.
Item B: Here it means "Although I am not very sure about my flexibility, I still went in with the guide" so use nonetheless "Even so", the position of however is wrong here (should not be placed in the verb and object), so item B is wrong.
Item C: wrong tense.
Item D: causality, the premise is that the author wants to explore by himself, but because he is not sure about his flexibility, he follows the tour guide, but follow ong will definitely happen here (because it is a tour guide ), so the latter sentence is not the previous result, and item D is wrong.