下面的句子来自2021年新高考考试全国乙卷（全国卷I）的完形填空，请问their指代哪个？
My parents thought all of this was a grand idea andcalled Betsy’s dad with their permission.
为便于理解，附整个段落如下：
My life as a tax-paying employed person began in middleschool, when, for three whole days, I worked in a baking factory. My bestfriend Betsy’s father was a manager at Hough Bakeries, which, at Easter time, madelittle bunny cakes for all its stores throughout Cleveland. Ithappened that the plant downtown needed eight kids for temporary help duringour spring break, for which I had no plans beyond listening to my favoriterecords. I’d earn minimum wage. I’d see how a factory worked. My parentsthought all of this was a grand idea and called Betsy’s dad with theirpermission.
My parents thought all of this was a grand idea andcalled Betsy’s dad with their permission.
依据上下文，我的理解为：我爸爸妈妈给Betsy's 的父亲打了个电话，表示他们赞同。their 指my parents。
从句子结构来看，非常显然 and 后面省略的主语是 my parents：
My parents called Betsy’s dad with their permission.
= My parents called Betsy’s dad to give theirpermission.
意思是：我爸爸妈妈打电话给贝蒂的父亲，告诉贝蒂的父亲他们赞同（我去做这项临时的工作）。
这篇文章源于美国《读者文摘》网站，如有兴趣，可以看一下。https://www.rd.com/article/editors-note-bunnies-on-the-line/
为了便于网友理解, 请看这句：
He arrived with good news.
其实这个句子结构和问题句是同样道理。
My parents called her Dad with their permission.
假如直译就是：我爸爸妈妈携带他们的许可给Betsy的父亲打了电话。这是由语境决定的思维逻辑。
