单选题 ______ you have already registered for the 2007 Forum, attend this free pre-forum class.
A. Although
B. Regarding
C. As
D. If

【正确答案】 D

【答案解析】中级问题只要出现两个“S+V”，就要考虑填入连词!B选项是介词，应排除。剩下的都是引导状语从句的连词，答案就要通过释义来判断。