If you use the phrases “one of… / each of… / any of…” they must be followed by the plural. Think about it – it’s logical. You’re always referring to one of / each of / any of many.

WRONG
We understand that one of the Company’s activity is financing the business activity of the companies from its group.

RIGHT
We understand that one of the Company’s activities is financing the business activity of the companies from its group.

WRONG
One of the most important selection criterion is the Personal Statement, which is as important as the interview.

RIGHT
One of the most important selection criteria is the Personal Statement, which is as important as the interview.

WRONG
Information sheets are available for each of the category covered by the rule.

RIGHT
Information sheets are available for each of the categories covered by the rule.

WRONG
We will charge you a blended hourly rate of EUR … plus VAT for work performed by any of our lawyer.

RIGHT
We will charge you a blended hourly rate of EUR … plus VAT for work performed by any of our lawyers.