他正在使用双显示器。

He is using ___dual monitors.

这把刀具有双重功能，既可以切菜也可以开瓶。

This knife has a ___dual function for both chopping and opening bottles.

这款手机有双卡功能，方便商务人士使用。

This smartphone has a ___dual-SIM feature, which is convenient for business people.