About the vocabulary in the book is ok but not very easy to learn as in books of Norman Lewis (they're holly grail for English learners anyway, I recommend to learn word power made easy first to lay the foundation for understanding of English roots).
The true thing that I am so sad about is the propaganda of anti-communism and the spreading of false information of the American government has been implanted cleverly in the book as a disguise of the reading text. several reading paragraphs talking about how great dr. Dooley was fighting against the sinister communist, how he rescued many Vietnamese from the malice of Viet Minh (probably he was a good man) as those Vietnamese were malnourished, sick and neglected. I am a Vietnamese myself and I had a long time studying and working in southern Vietnam and met a lot people there and no one ever described their post-war situations as bad as it is portraited in the book's reading sections. Yes they were suppressed and somewhat neglected since most of them were working or family members of people working for the American government but they did not need to be cared for since their situations were not as devastated as Vietnamese live in the north and central regions or Vietnamese family under Viet Minh, yes they were sick as every other Vietnamese at that time (we were super poor and did not have any facilities to produce medicine because of the bombing, most of the small quantity of medicine were from China and Soviet Union) and yes, they were suffered bad mistreatments like pillage and vandalism but they were not malnourished or killed or tortured like as other Viet Minh Vietnamese under the hand of the American army. The Viet Minh at that time didn't destroy the rice field and the southern part is the richest land in term of producing food (mostly rice), they would never suffer hunger as they just had to go to the river and get some fish (the river is running through every part of the southern land and it's tremendously abundant of aquatic products). On the other hand, people from the northern and central Vietnam governed by Viet Minh were the ones died of hunger and suffered form malnutrition the most and all the time as the bombing pouring everyday, many times a day causing huge lost to human and property, furthermore the lands (except region around Hong delta) are barren with hash weather.
For some people who are still skeptical of what I say, you can google it yourself about American war crime or you can ask any southern Vietnamese in America for there are a lot of them migrating to America (but to be honest they or their senior family members were only Vietnamese got benefits from American and did not get killed or tortured during wartime from both sides), or those in Vietnam if you come to visit Vietnam sometimes or for the best, visit War remnants museum in Ho Chi Minh city you will know what true evil is (most of the pictures were captured by western journalist.
Sorry for writing something that is mostly unrelated to the book but I was so emotionally grieved to see the victims who had to bear the heavy burden from the war were the ones to blame while the one raising war in other countries for no reason was painted as a saint.