4. 解析：选B。考查名词性从句。it作形式主语，指代后面的that从句。based on practice是过去分词短语作定语。

3. 解析：选D。过去分词短语作定语修饰experiments，experiments和carry out呈被动关系。

2. 解析：选C。句意为：如果你专注于手头的工作,你很快就能完成。apply oneself to ...专心于……,专注于……。

5. To my great delight, my son passed the examination.

提升练习

4. The professor came into the lecture hall accompanied by several assistant teachers.

3. The employees’? demand for higher pays was turned down by the employer.

2. When you apply for a job to the boss/employer, you should offer your information in detail.

5. was superior to

4. springing up

3. be wound up