21D6 B
 What number will a ship station use to identify itself using SITOR (NBDP)?
A. Four digit SELCAL.
B. Five digit SELCAL or 9 digit SELCAL number identical to MMSI.
C. 9 digit Inmarsat-B I. D. number.
D. 9 digit Inmarsat-C I.D. number.
