| List-I | List-II | ||
| (A) | Producer→ Consumer | (I) | One level |
| (B) | Producer → Retailer → Consumer | (II) | Three level |
| (C) | Producer → Wholesaler → Retailer → Consumer | (III) | Direct level |
| (D) | Producer → Agent → Wholesaler → Consumer → Retailer | (IV) | Two level |
What comes next in the series?
\(2, 6, 12, 20, 30, \ ?\)