Option D is correct. The first part 'I am trying to' (present continuous) shows an ongoing, current effort. The second part 'I can't remember' (present modal) states the current inability. Option A 'try to' is grammatically awkward and 'can remember' contradicts the meaning. Option B 'am not remembering' is incorrect - 'remember' is stative. Option C 'tried to' (past) doesn't match present context.