Answer from cs61c-cg (Daniel Lau 16776873) for Question 1
I don't really know what the question is asking for but i think the 2 differences are 
1. adding multiple operands: In C we can do it in a single instruction, while in MIPS we have to do 2 at a time because the number of arguments is fixed to 3.

2.When we want to access the member of the array in C and do operations to it, we just have to take the array element like this array[i] and work on it. But in MIPS we have to load the value into registers using lw command first.

their purpose is to make everything into the register so that the program can run faster.