Explanation:

- Option 1: Execution proceedings only

- Section 15 of the Limitation Act, 1963 is not limited to execution proceedings.

- Option 2: Suits only

- This section does apply to suits. It allows for the exclusion of certain periods when computing the limitation period for filing suits.

- Option 3: Appeals only

- Section 15 does not apply specifically to appeals.

- Option 4: Both (a) and (b)

- It applies to both suits and execution proceedings, allowing for time exclusions in certain situations like when an injunction or the stay order was in force.

- It doesn't apply to appeals but covers suits and execution of decrees.

Correct Answer: Option 4: Both (a) and (b)