The old lady was nervous, ________ she wasn't used to strangers calling late at night．

The old lady was nervous, ________ she wasn't used to strangers calling late at night．

A.and

B.for

C.but

D.so

答案及解析： B

考查连词用法。此处for意为“因为”，表示补充说明。不可位于句首。