[Business Translation (Advanced - ITT Level 1,2)] To teacher Grace

Hello Grace! I would like to ask you about the question 4 of ITT Test. My answer is exactly the same as the correct answer but you said  the preposition 'of' is correct and  gave me only 1.50.
Honestly I don't think that there is any grammatical error in my sentence and I think that it's very unfair to get only that score for my answer.