Why did gregor turn into a cockroach

There is no reason given for Gregor Samsa's transformation.

Explanation:  The opening lines are as much explanation as is ever given; the characters in the book show less surprise at the actual event and more disgust that Gregor is a giant insect. The metamorphosis itself is simply a given; there is no justification, or any reason that Gregor's human mind remains intact. Even Gregor himself is not so worried about the change:

"This getting up early," he thought, "makes one completely idiotic. A man must have his sleep. Other travelers live like harem women."

check your question

a) he encouraged islamic schools to introduce greek texts.

d) he invited greek scholars to teach their texts to the locals.

explanation: