Answer:
D. The Code Talkers received a medal.
Step-by-step explanation:
Option D is actually the least important to include in a summary.
A summary should contain the main idea of the passage. From the passage, we will discover that the main idea of the passage is likely the ability of Navajo soldiers to hide American codes from being cracked. So, when writing the summary, the problem should be briefly stated as a result Option A is important. Also, the nature of the Navajo language should be stated as an overview of what the language is all about; therefore, Option B is very important. Then the accomplishment of the Code Talkers will be included to round up the summary.
So, Option D is actually least important.