Which of the following for loop declaration is not valid?

• A. for ( int i = 99; i >= 0; i / 9 )
• B. for ( int i = 7; i <= 77; i += 7 )
• C. for ( int i = 20; i >= 2; - -i )
• D. for ( int i = 2; i <= 20; i = 2* i )