信用证对提供运输单据要求：“full sets 0f original clean on board ocean bill of lading made out to order 0f Royal Bank Canada and marked Freight Prepaid notify applicant．”这表示出口方提供的提单必须是(    )。
A、三份正本提单
B、清洁提单
C、通知人显示“applicant”
D、已装船承运人提单
E、收货人显示“to order of Royal Bank Canada”