A car salesperson earns a monthly base salary plus commission for every car he sells. The expression gives the amount the salesperson earns if he sells x cars in a month.

To find the commission the salesperson earns for each car sold, we can look at the expression:

\[ 2,000 + 1,000x \]

In this expression:
- \(2,000\) is the base salary.
- \(1,000x\) represents the commission earned for selling \(x\) cars.

The coefficient of \(x\) (which is \(1,000\)) indicates the amount of commission earned for each car sold.

Thus, the correct response is:

B. $1,000