Answer:
D) Use of contractions
Explanation:
You should try to avoid using contractions when you are writing a formal report, since their use tends to give a sentence a less formal tone, besides making it shorter. When you are speaking, contractions are not considered informal, but it is not the same with writing. In business, contractions are used mainly for advertising since you generally pay for the space or time you use, and it is an advantage to make shorter phrases.