那是这本书的中心论点。

That is the central ___thesis of the book.

这个论点不仅适用于音乐，在我看来，也适用于许多其他生活领域。

This ___thesis applies not only to music but, in my opinion, also to many other walks of life.

他的博士论文挑战了该领域几个长期持有的假设。

His doctoral ___thesis challenged several long-held assumptions in the field.