From a strictly economic perspective, immigration should be

A) expanded until its marginal benefits equal its marginal costs.
B) expanded until its total benefits equal its total costs.
C) expanded as long as its marginal costs exceed its marginal costs.
D) reduced if its marginal benefits exceed its marginal costs.

From an economic standpoint, the optimal point for any activity, including immigration, is reached when its marginal benefits equal its marginal costs. This ensures that the activity is maximized to the point where the last unit provides as much benefit as it costs, without going over into a zone where the costs would start to outweigh the benefits.