I really enjoyed your talk, ________ there were some parts I didn’t understand.

A．because

B．unless

C．though

D．after

证券公司应当在营业场所妥善保存有关介绍业务的凭证、单据、账簿、报表、合同、数据信息等资料。证券公司保存上述文件资料的期限不得少于( )年。

A．3

B．5

C．10

D．15