ANS:A - higher economy

A backward feed multiple effect evaporator is better than forward feed for concentrating cold feed because it provides higher economy. In a backward feed multiple effect evaporator, the feed is introduced into the last effect of the evaporator series and progresses backward toward the first effect. This arrangement allows for better utilization of the available temperature difference across each effect, leading to higher energy efficiency and, consequently, higher economy compared to a forward feed arrangement. Therefore, the correct option is: higher economy.