8.
Your Answer is
Correct Answer is G
Explanation
According to the meaning of the sentence "They have arrived in New Guinea and completed three-quarters of the flight, when the outside world lost contact with them..." Judging that the underlined part is followed by an adverbial clause of time, it should be used when, item G is correct .
Item H: while needs to be consistent in tense before and after. because table cause and effect, error. After means that the following sentence occurs first, that is, the sentence guided by after should use the past perfect tense, which is wrong.