$20. \_ the difficult math problem, I have consulted Professor Russell several times.$
Answer key
C
_ the difficult math problem,…——2014 高考英语第 20 题答案解析
2014_省自主命题（陕西）
题目指纹
这道题真正考什么？
difficulty
Differentiating
2014_省自主命题（陕西）
$20. \_ the difficult math problem, I have consulted Professor Russell several times.$
C