There are several factors in the economy make it difficult to predict the future.
A. operate; where
B. operating; which
C. to operate; that
D. operated; what
网友回答
A. operate; where
(答案→)B. operating; which
C. to operate; that
D. operated; what
解析：本题考查非谓语动词及定语从句。名词factors与operate的关系为主动关系，用现在分词，后一空为定语从句，先行词为factors，在定语从句中作主语，故选B。