Explanation:

- Option 1 states that the Code of Criminal Procedure (CrPC) is mainly, though not purely, an adjective or procedural law. This is correct. The CrPC lays down the procedure for investigation, trial, and punishment of offences.

- Option 2 says there are also certain provisions which are partly in the nature of substantive law. This is also correct, as some sections, like those granting powers to courts to grant bail or compensation, have substantive impact.

- Option 3, both (a) & (b), is correct because both statements accurately describe the CrPC.

- Option 4, neither (a) nor (b), is incorrect because both (a) and (b) are true.

Option 3 is the correct answer.