What was a main advantage of the three-field system?

crops matured at different times.
new types of crops could be grown.
extra food reduced the chance of famine.
multiple harvests became commonplace.

Extra food reduced the chance of famine.

Explanation:

the correct answer is:   "   3.6 % " .

          →   the unemployment rate is:   " 3.6 % " .

explanation:

to calculate the "unemployment rate" :

the "unemployment rate"   =

  [# of people unemployed] /   [working age population]   * 100 %   ;

                =   [9 million] / [250 million]     *   100 % ;

    →     note:   the units of "million" cancel out;

                    since:   " {million} / {million} = 1 " ;

                =   (9 / 250)   * 100 %   ;

                = 0.036 * 100 % ;

                =   3.6 %

answer:   the unemployment rate is:   " 3.6 % " .

the answer is they believed george iii would never give them their freedom.