下列对信用证有效期的描述，属于直接写明具体日期的是（） A: Documents must be presented for negotiation within 10 days after the on board date ofbill of lading B: Negotiation must be on or before the 15th day of shipment C: This L/C is valid for negotiation in China until Oct. 1, 2002 D: Documents to be presented to negotiation bank within 15 days after shipment