Mark the letter A, B, C, or D to indicate the underlined part that needs correction in each of the following questions.

 They had visited Ho Chi Minh Mausoleum at this time last Sunday.

                     A                                       B        C                  D

It was such a difficult homework that it took me two hours to finish it.

            A          B                                  C                                           D

The first national park in the world, calling Yellowstone Park, was established in 1872.

        A                               B                      C                                                 D

The package must be wrapped carefully before it is post.

                 A                     B                                C           D

Of all the portraits he has painted, I like this one more.

    A                                         B             C                   D

The teacher asked him why hadn't he done his homework, but he said nothing.

                                              A              B                                     C              D

Even on the most careful prepared trip, problems will sometimes develop.

         A                            B                     C                                       D