电工正在检查房屋的主电源线路。

The electrician is checking the ___mains wiring in the house.

工人们正在修理大楼的主水管。

The workers are repairing the ___mains of the building.

今晚我们提供两种主菜：烤鸡和蔬菜派。

We have two ___main dishes for dinner tonight: roast chicken and vegetable pie.