题目选项分析

[span]If the airspace around centrally located airports were restricted to commercial airliners and only those private planes equipped with radar, most of the private-plane traffic would be forced to sue outlying airfields. Such a reduction in the amount of private-plane traffic would reduce the risk of midair collision around the centrally located airports.[/span]

The conclusion drawn in the first sentence depends on which of the following assumptions?

【选项】Most private planes that use centrally located airports are not equipped with radar.