According to the passage, proponents of the use of genetically altered bacteria in agriculture argue that which one of the following is true of the altered bacteria used in the frost-damage experiments? A. The altered bacteria had a genetic constitution differing from that of the normal strain only in that the altered variety had one less gene. B. Although the altered bacteria competed effectively with the nonaltered strain in the laboratory, they were not as viable in natural environments. C. The altered bacteria were much safer and more effective than the naturally occurring Pseudomonas fluorescens bacteria used in earlier experiments. D. The altered bacteria were antagonistic to several types of naturally occurring phytopathogens in the soil surrounding the roots of frost-damaged crops. E. The altered bacteria were released into the environment in numbers sufficient to guarantee the validity of experimental results.