This is the only one of the oldest customs that ________ down in this area so far.

This is the only one of the oldest customs that ________ down in this area so far.

1. A.
   was kept
2. B.
   were kept
3. C.
   has been kept
4. D.
   have been kept

 This is the only one of the oldest customs that ________ down in this area so far.

       A. was kept         B. were kept

       C. has been kept     D. have been kept

This is the only one of the oldest customs that ________ down in this area so far.

       A. was kept    B. were kept

       C. has been kept     D. have been kept

This is the only one of the oldest customs that ________ down in this area so far.