The answer is C. Central processing unit (or CPU).
The trick is in the name, central processing unit :)
A higher frequency than the analog cell phone.
The answer is 2-to-the-power-of-n, since for every input, the number of different combinations doubles. From your list I think answer A is meant to indicate 2ⁿ.
The answer is Themes. A theme is a set of colors, fonts, and effects that establish closely the overall look of your document. Themes are a great way to change the tone of your entire document quickly and easily. It is a set of formatting choices that can be applied to an entire document.