While the discovery brought hope and joy to everyone, the rescue
mission was far from over.

The passage they had used to enter the cave
was now completely submerged, making it impossible to follow the
same route back.

Moreover, the boys had to dive for approximately five
hours through narrow and dark waters to get out, which was an
extremely challenging task even for the most proficient divers.

Furthermore, many of the boys were weak from their time in the cave
and most of them could not swim.

The passage they had used to enter the cave was now completely submerged, making it impossible to follow the same route back.

The passage는 문장의 주어이며, 생략된 목적격 관계대명사 which[that]가 이끄는 절이 이를 꾸며 주고 있다. make it impossible to follow 구문에서 it은 가목적어, to follow 이하는 진목적어로 ‘같은 경로로 되돌아 나오는 것을 불가능하게 만들다’라는 뜻이다.

Moreover, the boys had to dive for approximately five hours through narrow and dark waters to get out, which was an extremely challenging task ~.

for는 시간의 전치사로 ‘…동안’을 의미하며, through는 공간의 전치사로 ‘…을 통과해’를 의미한다. 주격 관계대명사 which는 앞 문장 전체를 보충 설명하는 계속적 용법으로 사용되었다.

That way, I wouldn’t be stuck with a bunch of physical gifts that I didn’t want.

목적격 관계대명사 that이 이끄는 절이 선행사 a bunch of physical gifts를 부연 설명하고 있다.

Parents, teachers, friends, and others you trust can also provide insight into you that you may not have noticed.

you trust 앞에 목적격 관계대명사 that이나 which가 생략되어 있으며, you trust는 Parents, teachers, friends, and others를 수식한다.

that은 목적격 관계대명사로, insight를 선행사로 한다.

<may not have + p.p.>는 과거에 대한 추측을 나타내는 표현으로, ‘~이 아니었을지도 모른다’라는 뜻이다.