문법문젠데요~
 To summarize an article is to separate __________ which is essential from the supporting material that surrounds it.

정답은 that 인데요 문법적 구조를 잘 모르겠어요~

___________________ 답 변 _______________

that which=what의 의미입니다. 즉 what is essential ---로 이해하면 됩니다.

She insists it is (I) who (am) mistaken about the effect of the order on those who have (less) responsibilities than (I).

답은 less를 fewer로 고치는 건데 I who am 부분 좀 설명해주세요^^

_________________ 답 변 __________________

it is I that am mistaken --은 it -- that 강조구문입니다. 여기에서 I를 강조하기 때문에 that 대신 who를 쓴 것입니다.

In  (ancient) times, books came in cumbersome packages and could not (be carried) under (an) arm or read (on way) to work.

정답은 4번인데 왜그런지 설명좀 해주세요~~^^

____________________ 정 답 __________________

'직장에 가는 도중에'의 으미는 on the way to work이므로 on the way를 써야하겠네요.