In English, we say that the "eyes drifted shut" to express and show how the person closed their eyes without actively thinking or wanting to shut them. When you "drift", you do so without doing it forcefully. That is why we have the expression "drifted shut" to indicate that the eyes closed at some point before the person knew. Taboo is something that society prohibits or something that everybody refuses to talk about because the topic is sensitive or highly controversial. I think the sentence you have is trying to show that talking about other people's salaries and wages (the money they get from work) is highly personal so it is considered a "taboo" topic (in western culture at least). Lori Lemon is probably a fictional name used in the book or exam you are using here. Arched, by itself, means something curved. It is a physical description. "Arched away" is a description of motion to show that something/ someone has moved backwards away from something. Hope this helps!

Third sentence: It is similar to saying "Lori Lemon thought that the doctors were flabbergasted." One way of stating your opinion on something is to say "It seems to me that _________." (putting your opinion in the blank.) Here we have "It seemed to Lori Lemon that the doctors were flabbergasted." But the sentence is rearranged for emphasis. The phrase isn't "all seemed" but "doctors all" which means every one of the doctors.

1. Drifted =slowly slowly moved 2. The taboo (topic) is wages. In thè sentence you submitted, "taboo" is the subject when normally it is used as an adjective. But though it is an unusual construction, the meaning implies 'taboo topic' 3. The third sentence does not make sense to me 4. The difference between arched and arched away ... hard to explain without context.