Defending Old Testament Authorship

How true is the Old Testament? For over two centuries Biblical scholars have held to the so-called documentary hypothesis, namely, that Genesis-Deuteronomy was not authored by Moses, but rather by several writers, some of whom lived centuries after Moses' time. How have many scholars questioned the writership of Isaiah, and are they correct? When did skepticism regarding the writership of Isaiah begin, and how did it spread? What dissecting of the book of Isaiah has taken place? When did criticism of the book of Daniel begin, and what fueled similar criticism in more recent centuries? What charges are sometimes made regarding the history in Daniel?Why is the question of the authenticity of the books of Moses, the Book of Isaiah and the Book of Daniel an important one? What evidence is there to show that the books of Moses, the Book of Isaiah and the Book of Daniel is authentic and true? Do these critics have grounds for challenging these Bible author's authenticity and historical truthfulness? Why is it important to discuss whether Old Testament Aurhoriship is authentic and true or not?