sunglasses单数还是复数？

　　例句：

　　1、These sunglasses are designed to reduce glare.

　　这些太阳镜是为减少刺眼的强光而设计的'。

　　2、 The sunglasses is used to filter the light.

　　太阳镜用于滤光。

　　3、I wore sunglasses all the time and people thought it was an affectation

　　我成天戴着墨镜，大家都觉得我在装酷。

　　4、I packed your sunglasses with the green lenses.

　　我把你那副绿色镜片的太阳镜装好了。

　　5、 She slipped on a pair of sunglasses.

　　她迅速戴上一副太阳镜。