问题补充：
Hello! I you in London. How long have you been here?
A. don’t know, were
B. hadn’t known ,are
C. haven’t known ,are
D. didn’t know, were
答案：
A. don’t know, were
B. hadn’t known ,are
C. haven’t known ,are
(答案→)D. didn’t know, were
解析：考查时态.根据下文你在这儿多久了?可知前文意思是我不知道你在伦敦.说的是在这以前我不知道你在伦敦,主从句都是强调的过去,故选D.
