ships trAvEling in thE northAtlAntiC During thE wintEr must BE ConstAntly wAtChFul to AvoiD iCEBErgs, lArgE mAssEs oF iCE ______ only onE-ninth is visiBlE ABovE wAtEr.
A、so thAt B、in thAt
C、whiCh
D、oF whiCh