Which questions would improve the readers ability to understand the military leaders fear that the code wouldn't no longer be effective

Although American Indian soldiers had effectively used their languages to create and transmit secret messages during World War I, military leaders were reluctant to use the code a second time, fearing that it would no longer be effective. The Japanese and German governments had sent students to the United States specifically to learn certain American Indian languages. The Navajo language, however, was so complex that few people outside the Navajo Nation itself could speak it. In 1942, it was estimated that only thirty non-Navajos spoke the language worldwide.