It was then decided that Alan Shepard should relieve himself in his space suit, and continue with the mission as scheduled. 22 problem urged NASA to develop the first space toilet, a modified diaper.
答案：(B) This
This 指代前文提到的問題（雪帕德必須在太空衣裡如廁），This problem 承接上文；Each（每個，不指代特定問題）、Their（他們的）、Another（另一個，語意不合，這裡指的正是前面提到的同一個問題）都不合。
四個選項擺進去都成句：Each problem、This problem、Their problem、Another problem，沒有一個違反文法。這種時候很容易憑語感挑一個，而 Another problem（另一個問題）讀起來特別順，因為前面確實出了狀況，感覺「又來一個」。但這一格不是要你再開一個新問題，是要你把剛剛那個問題收攏起來再指一次。
四個選項都是擺在名詞 problem 前面的限定詞，可見這一格考的不是文法而是「這個 problem 到底指什麼」，那就得回頭讀前一句。前一句是 It was then decided that Alan Shepard should relieve himself in his space suit（於是決定讓雪帕德在太空衣裡解決），這件事本身就是一個問題。用一個比較概括的名詞（problem）把前面剛講過的內容收攏起來再指一次，前面就要加 this，這叫回指（Halliday 與 Hasan「Cohesion in English」的指稱銜接）。判斷的順序是先問「this 指的是前面哪一段」，再看四個選項哪一個接得住（同型：94 年第 28 題的 this discomfort 回指前文的 feel pain）。這一題的鑑別度 46，分開的就是有沒有動手把 this 的所指釘回前一句。
Another（另一個）：它預設前面已經出現過同類的問題，而這是別的一個；但本句指的正是剛剛那一個，方向相反。Each（每一個）：要有一組複數的問題可以一個一個分配，前文只講了一件事。Their（他們的）：前文沒有出現一群人來當這個 their 的所指，被決定的是任務怎麼進行，不是誰的問題。
solve a problem（解決問題）、pose a problem（造成問題）、run into a problem（碰上問題）、urge sb to V（力促某人做……）、a modified version（改良過的版本）、cause trouble（惹麻煩）。
The first American space toilet was Alan Shepard's space suit. His flight was supposed to last only 15 minutes, so there was no provision made for him to relieve himself in the capsule. His flight, 21, was delayed for hours. It was then decided that Alan Shepard should relieve himself in his space suit, and continue with the mission as scheduled.
22 problem urged NASA to develop the first space toilet, a modified diaper. Diapers are 23 used by astronauts when they are outside the space shuttle, wearing a spacesuit.
As the flights grew longer, a new set of two collection bags was devised, 24 for liquid wastes and the other for solid wastes. Once used, the bags are sealed and stored for the flight back to the earth, 25 they are disposed of.