The economic importance of Ethiopian lakes and rivers

F=31 because you subtract 39-8

Ais the answerhope it

Most topographic maps, the index contour lines are generally darker and are marked with their elevations. 

It's either  a. chiang kai-shek and the nationalists turned against the communists and killed hundreds of them. orb. hundreds of peasants were killed in shanghai during the period of warlord rule.  if we take into account that there was warlord rule at the time, i think that it's b (not entirely sure though)just my best thoughts.