C. in
Feedback We should remember that some nouns are used with specific prepositions after them. After the noun ‘difficulty’ (pl. difficulties) that means ‘something that is not easy to deal with; a problem; a thing or situation that causes problems’ we can use tree prepositions: ‘in’ (There are some difficulties in learning prepositions in English.), ‘with’ (Some students have run into difficulties with the new project.; There are some typical difficulties with prepositions in English.) and ‘of’ (The difficulty of the situation made him feel helpless.). Therefore, among the test answers we are to choose ANSWER 3: ‘in’.