86. The primary purpose of the passage is to ____.

1. expose the fragile nature of the foundations on which the high yields of modern agriculture rest
2. argue that genetic engineering promises to lead to even higher yields than are achievable with synthetic fertilizers
3. argue that the capacity for nitrogen-fixing symbioses is transferable to non-leguminous plants
4. explain the reasons for and the objectives of current research in nitrogen-fixing symbioses

87. According to the passage, there is currently no strain of Rhizobium that can enter into a symbiosis with ____.

1. alfalfa
2. clover
3. maize
4. peas

88. The most influential factor in bringing about intensified research on nitrogen fixation is ____.

1. the high yields of the Green Revolution
2. the persistent upward surge in natural gas prices
3. the variety of Rhizobium strains
4. the mechanization of modern agriculture

89. According to the passage, the ultimate goal of the current research on nitrogen fixation is to develop ____.

1. strains of Rhizobium that can enter into symbioses with existing varieties of wheat, rice, and other non-legumes
2. strains of Rhizobium that produce more ammonia for leguminous host plants than do any of the strains presently known
3. varieties of wheat, rice, and other non-legumes that yield as much as do existing varieties, but require less nitrogen
4. varieties of wheat, rice, and other non-legumes that maintain an adequate symbiotic relationship with nitrogen-fixing bacteria and produce high yields

90. The author regards the research program under discussion as ____.

1. original and extensive but ill-defined as to method
2. necessary and ambitious but vulnerable to failure
3. cogent and worthwhile but severely underfunded
4. prohibitively expensive but conceptually elegant

(Reference keys.)