P1 - Special kinds of cotton that grow fibers of green or brown have been around since the 1930s
P2 - but only recently became commercially feasible
P3 - when a long-fibered variety that can be spun by machine was finally bred
P4 - Since the cotton need not be dyed
P5 - processing plants avoid the expense of dyeing
and
the ecological hazards of getting rid of leftover dye and by-products.
A - Ecologically safer is meant for all types of cotton
B - Brown or green cotton recently became commercially feasible when a long variety that can be spun by machines came into existence. Earlier brown or green cotton wasn't feasible when a short variety of the same was available. Thus the short varieties were not commercially feasible - Correct
C - Same as B - we have no idea about hand spun cottons - what varieties fell into hand spun category etc.
D - We are told only when long spun category came into existence that long or brown cotton were commercially feasible that could be spun by machines i.e. synthetic fibres. Earlier short varieties were not feasible for this reason. Hence they were not competetive
E - End products - garments is not discussed in the passage and can not be concluded
Answer - B