In the following chart, the price of logs shown is per cubic meter and that of plywood and saw timber is per ton. Given that $1$ cubic meter of Plywood and Saw Timber = $800$ kg ($1$ ton = $1000$ kg)
If $1$ cubic meter = $700$ kg for Plywood, in which year was the difference in the prices of plywood and saw timber the minimum?
- $1989$
- $1990$
- $1991$
- $1992$