Explanation:

- Option 1: It is mainly, though not purely, an adjective or procedural law.

- This means the Code of Criminal Procedure primarily deals with the processes of legal proceedings but is not exclusively about procedures.

- Option 2: There are also certain provisions which are partly in the nature of substantive law.

- This indicates that the Code includes some sections that establish rights or obligations instead of just detailing procedures.

- Option 3: Both (a) and (b).

- Correct Answer: The Code of Criminal Procedure contains both procedural regulations and some elements of substantive law.

- Option 4: Neither (a) nor (b).

- This would mean the Code is neither adjective nor includes any substantive elements, which is incorrect.