    Sentence 1; Searches for survivors. from  ‘several previous.-shipwrecks .have often  had to be abandoned for similar reasons ,  leaving the vessels and» most of -their  passengers unaccounted for .    Sentence 2: In. several. previous  shipwrecks , the search for survivors had  to. be ‘abandoned for similar reasons: ,  leaving the vessels and most of their  passengers unaccounted for .