三、用方框中所给单词或词组的适当形式填空。每词（组）限用一次。
sick bad because discover scientist
for disease protect come up with
Many terrible diseases spread across Europe long ago. 21. there were no cures（治疗）, many people lost their lives.
The famous chemist Louis Pasteur spent years looking for reliable methods to 22. farm workers from deadly germs（细菌）. When he did farm experiments, he found local cattle handlers rarely got very 23. and they usually did not die. Then he 24. some ideas and later carried out plenty of biological research. He 25. tiny bacteria were the root of most contagious（有传染性的）illnesses. He kept all his lab notes for other 26. to study. Back then, illnesses carried by farm animals were seen as one of the 27. dangers to villagers. His theory offered useful ways to cure all kinds of 28. across the world.
His great discoveries laid the foundation 29. modern vaccine technology worldwide. He is a real hero.

21. Because 22. protect 23. sick 24. came up with 25. discovered 26. scientists 27. worst 28. diseases 29. for

【分析】
做此类用方框中所给单词适当形式填空的题目，需结合句子逻辑、语法规则（时态、词性、固定搭配等）逐一分析每个空：
1. 21空：前后句为因果关系，句首需用表原因的连词；
2. 22空：此处表目的，用不定式结构，结合固定搭配“保护...免受”的用法，选对应动词；
3. 23空：get为系动词，后接形容词，结合语境“生病”的含义选对应词；
4. 24空：句子为一般过去时，“想出主意”需用对应词组的过去式；
5. 25空：句子为一般过去时，“发现”的动作需用对应动词的过去式；
6. 26空：other后接可数名词复数，“科学家”需用复数形式；
7. 27空：one of后接形容词最高级，“最严重的”需用对应形容词的最高级；
8. 28空：all kinds of后接可数名词复数，“疾病”需用复数形式；
9. 29空：结合固定搭配“为...奠定基础”选对应介词。
【解析】
根据上述分析，结合语法规则和语境，各空答案推导如下：
21. 前后句为因果关系，句首用连词Because（首字母大写）；
22. 不定式符号to后接动词原形，结合固定搭配protect...from，选protect；
23. 系动词get后接形容词，结合语境选sick；
24. 一般过去时，come up with的过去式为came up with；
25. 一般过去时，discover的过去式为discovered；
26. other后接可数名词复数，scientist的复数为scientists；
27. one of后接形容词最高级，bad的最高级为worst；
28. all kinds of后接名词复数，disease的复数为diseases；
29. 固定搭配lay the foundation for，选介词for。
【答案】
21. Because 22. protect 23. sick 24. came up with 25. discovered 26. scientists 27. worst 28. diseases 29. for
【知识点】
动词适当形式填空、固定搭配、形容词最高级
【点评】
本题为英语词汇语境运用题，考查学生对词汇的词性、时态、形式变化及固定搭配的掌握，需结合上下文逻辑和语法规则解题，难度适中。
【难度系数】
0.4