One of the four underlined parts marked A, B, C, D in each sentence is not correct in standard English. Identify them

Exercise 4: One of the four underlined parts marked A, B, C, D in each sentence is not correct in standard English. Identify them.
1.      If Lucia had been here now, she would find out the truth about her uncle’s accident.
             A                                      B                                C                D
2.      If a student takes a course on Computer Science, it will take him four years doing the course.
      A                          B                                                            C                              D
3.      Unless it did not rain, Peter would pay us a visit.
          A                 B                             C                D
4.      If had I known you were in financial difficulty, I would  help you.
                 A                    B    C                                                 D
5.      If she had finished the work, she can go home.
                        A               B                      C    D                                                                      
6.      If we had had a map, we would not be lost yesterday.
      A            B                              C            D