Answer from cs61c-el (David Tung 16479725) for Question 1
The C preprocessor, if it were shown in the chart, would be right before the compiler.  Its purpose is to just make some constants more obvious, or to create macros to make complicated tasks that need to be repeated more succinct and compact.  It takes as input a C program, and outputs a C program, because it does not really interpret or change the program, it just replaces certain text segments.