房子是大多数人一生中做过的最昂贵的购买。

A house is the most expensive ___purchase that most people ever make.

对枪支的购买实施了新的限制。

New restrictions have been placed on the ___purchase of guns.

您无需购买任何产品即可参加本次竞赛。

No ___purchase is necessary for you to enter this competition.