a group of…作主语时，谓语动词用单数还是复数

下面一句：

A group of children _____ sitting around playing cards.

A. was B. were

选A还是选B？换句话说，a group of…作主语时，谓语动词用单数还是复数？谢谢！

答案可以选A也可以选B。即a group of…作主语时，谓语动词可用单数也可用复数。如：

1. A group of women were cackling in a corner. 一群妇女在角落大笑。——源于《剑桥高级英语词典》；谓语用复数were。

2. A group of her friends was waiting for her inside. 她的一群朋友在里面等她。——源于《麦克米伦高阶美语词典》；谓语用单数was。

3. A group of girls was [were] waiting at the school gate. 一群女生在校门口等着。——源于《现代英汉词典》外研社；谓语用单数和复数was / were。