Typically, 3D chips are created by layering individual ____ wafers on top of one another with a special machine that uses cameras to align the wafers properly.

In __________ mode the I/O module and main memory exchange data directly, without processor involvement.

Fill in the blank(s) with the appropriate word(s).

Which of the following creates the string of the numbers from 1 to 1000 most efficiently?

a. ``` String s; for (int i = 1; i <= 1000; i++) s += i; ``` b. ``` StringBuilder sb = new StringBuilder(10); for (int i = 1; i <= 1000; i++) sb.append(i); String s = new String(sb); ``` c. ``` StringBuilder sb = new StringBuilder(3000); for (int i = 1; i <= 1000; i++) sb.append(i); String s = new String(sb); ``` d. All are equivalently efficient.