By 1935 the proportion of women workers in the ussr’s workforce was in every five.
a. one
b. two
c. three
d. four

The answer is one in every five 

Two in every five.

In the 1920s, the percentage of women in the USSR's workforce was about 1 in 4 -- remaining around 28% through most of that decade.  But those numbers would increase under the First and Second Five-Year Plans instituted by Joseph Stalin.  By 1935, the percentage of women employed in large-scale industry in the Soviet Union had grown to 40%  (representing two out of every five workers).  

For further information and detail, you might consult the book, The Position of Women in the USSR, by G.N. Serebrennikov (published 1937).