TOEFL Grammar - Find the error

ScottsEnglish

Find the error in the underlined words in the following sentence:

Her recent research has been very influenced in the field, so much so that new textbooks are being written around the conclusions of her studies.

A. recent research
b. very influenced
c. so much so
d. written around

Her recent research has been very influential in the field, so much so that new textbooks are being written around the conclusions of her studies.