参考答案：D

解析：理解推断。题干：弗兰克有几个孩子 根据原文“Frank introduced me to his wife and even invited me to spend the fourth of July together with his eight children and grandchildren．”，译文为：弗兰克把我介绍给他妻子，并邀请我和他的8个孩子和孙子一起过国庆节。所以根据原文可知弗兰克共有8个子孙，但不知他到底有几个孩子，所以选d。