Explanation:

Here’s the thing:

- Option 1: Quantity audit

This looks at numbers—how much or how many—so it checks volumes, counts, or amounts. It doesn't get into how well the whole system works.

- Option 2: Quality audit

This covers much more. A quality or system audit reviews if the system as a whole is suitable, effective, and meets requirements. It’s not just about products; it’s about processes, culture, and results.

This is the most comprehensive type of audit.

- Option 3: Preliminary audit

That’s just an initial review. It comes before the main audit and is usually for getting a feel for what to expect. It’s nowhere near as in-depth.

- Option 4: Sequential audit

This means audits done in a certain order, not about how deep or broad the audit is.

So, the answer is clear:

Option 2 - quality is correct.