To determine the approximate straight-line distance between Darwin and Brisbane using the map's scale, I would need to reference the actual map you mentioned. Since I don't have the ability to view images or maps, I can't give you the exact measurement directly.
However, I can help you estimate the distance if you refer to the scale. If, for example, the scale indicates that a certain distance on the map corresponds to a specific number of kilometers, you can measure the distance between Darwin and Brisbane on the map, then use the scale to convert that measurement into kilometers.
If the distance measured (for example, in centimeters on the map) corresponds closely to one of the answer choices (2,500 km, 2,000 km, 1,800 km, or 1,500 km), you can select that option.
If you provide me with additional details about the scale and measurement, I could guide you more accurately!