李某和王某订立一购销合同，约定李某向王某预付货款5万元，王某负责将货物运至甲地，双方如发生纠纷，则由李某选择管辖法院。合同签订后，李某向王某开出了一张金额为5万元的银行承兑汇票，付款日期是1998年7月31日。　　双方关于选择管辖法院的协议是否有效

A．有效，李某可任意选择管辖的人民法院

B．有效，但李某只能在合同签订地、合同履行地、李某住所地、王某住所地人民法院中选择之一来起诉

C．无效

D．是否有效，要由王某决定

Which of the following factors would be most important in selecting the needle length to use for a subcutaneous injection of hydromorphone hydrochloride

A．The diameter of the needle.

B．The amount of adipose tissue at the administration site.

C．The amount of medication to be administered.

D．The viscosity of the solution to be injected.