The clock frequencies of common Intel CPU's used in laptop and desktop computer systems have not appreciably increased during the last 20 years or so. Why is this?

Reference: 1. Chapter 1 Lecture Notes 1.7

Group of answer choices

a) Because designers have not been able to manufacture smaller transistors.

b) Because higher clock frequencies cause processors to run too hot and they begin to fail.

c) Because designers have been unable to lower CPU voltage levels below 3.3 V.