超市正在促销牙膏，买一送一，这种优惠活动很划算。

The supermarket is offering toothpaste ___twofers - buy one, get one free, which is a great deal.

这位教授既是系主任又负责本科教学，真是个双料人才。

The professor serves as both department chair and undergraduate instructor—a true ___twofer.