The correct answer is $\boxed{\text{A}}$.
The selling price variance is calculated as follows:
Selling price variance = (Actual selling price – Standard selling price) * Actual units sold
In this case, the actual selling price is $400, the standard selling price is $250, and the actual units sold are 500. Therefore, the selling price variance is:
Selling price variance = ($400 – $250) * 500 = $45,000
Option B is incorrect because it is the difference between the actual selling price and the standard selling price per unit. Option C is incorrect because it is the product of the actual selling price and the actual units sold. Option D is incorrect because it is the sum of the selling price variance and the quantity variance.