Fill in the blanks left in the classification of the fossil fuels.
| q | u | v | w | x | ||
| A | Petroleum | Coal | Petroleum gas | Bitumen | Coal gas | Coke |
| B | Coal | Petroleum | Coal gas | Coke | Petroleum gas | Bitumen |
| C | Coal | Petroleum gas | Coal | Charcoal | Gasoline | Coal tar |
| D | Petroleum | Coal | Gasoline | Bitumen | Natural gas | Coke |