两个动名词作主语谓语用单数还是复数

Sitting and talking to old friends is a pleasant way to spend an evening.
请问这个句子为何不需要复数谓语动词 are，主语不是两个动名词 sitting 和 talking to old friends 吗？两个动名词作主语时，怎么分辨谓语动词是用单数还是用复数？谢谢老师！

▲Sitting and talking to old friends “坐着和老友交谈”是一个整体行为，故谓语动词用单数。
▲当作主语的两个并列的动名词表达一个整体意义时，谓语动词用单数；若表达个体意义时，谓语动词用复数。如：
Singing and dancing is inbred in children. 小朋友非常喜欢唱歌跳舞。（“唱歌跳舞”是整体意义）
Dancing and singing were among her many accomplishments. 她才艺双全，能歌善舞。（侧重“既能唱歌，也能跳舞”）