根据以下信用证条款回答40-42题：Applicant：Peter Flowers Corp., Netherlands 231 Merry Street Amsterdam, NetherlandsBeneficiary：May Flowers Corp., China 18 Chung Shan Road, Shanghai, ChinaDocuments required： Full set of clean on board ocean bills of lading made out to order and blank endorsed ，marked “freight prepaid”,notify applicant. 按提单收货人分类，该提单属于哪一种类？（ ） A: 记名提单 B: 不记名提单 C: 清洁提单 D: 指示提单