请教

Some of the tenth-century stave churches of Norway are still standing, demonstrating that with sound design and maintenance, wooden buildings can last indefinitely.

A  standing, demonstrating that with sound design and maintenance, wooden buildings can last indefinitely.

B  standing, demonstrating how wooden buildings, when they has sound design and maintenance, can last indefinitely.

C  standing, they demonstrate if a wooden building has sound design and maintenance it can last indefinitely.

D  standing, and they demontrate wooden buildings can lastin definitey when there is sound design and maintenance.

E  standing, and they demontrate how wooden buildings can last indefinitely when it has sound design and maintenance.

正确答案是A

我觉得应该在that后面加个逗号，with sound design and maintenance作为插入语，that后面直接跟 wooden buildings can last indefinitely

还是不加也行，不加的话怎么理解？

不用加逗号，因为with sound design and maintenance不是插入语，而是作状语修饰wooden buildings

插入语是修饰整个句子，而不是修饰句子中的某个成分