參考答案及解析:
1. with—without。根據illegal aliens的定義，應該是people living in the U.S.A without proper authorization
2. until—when。從邏輯意義上來分析，是Others....did not leave when their visas were expired（當簽證到期時他們也不離開美國）
3. possible—impossible。從上下文的說明判斷，要弄清楚到底有多少非法居住在美國的外國人，或得一個確切的數據是完全不可能的
4. ranged之前加have。因為是指did not leave until their visas were expired. Recent estimates而不是以往的estimates
5. affected—affecting。此處相當于（a new law）which/that affect illegal aliens
6. have—had。用過去完成時，因為整個句子討論的是過去的事，并且此處具體指country since January, 1982 to gain legal status if they applied by May 4,1988
7. encourage—discourage。如果為encourage則與全文的邏輯和意義矛盾
8. 在difficult之前加it。making it difficult for undocumented people to find employment，其中it為形式賓語，實際賓語為不定式短語（for undocumented people）to find employment
9. providing—provides。provides for severe penalties與prohibits American employers from hiring illegals 為并列謂語，而不是與hiring illegals并列
10. number—numbers或在large之前加a。習慣為numbers of或a number of