Answer from cs61c-eg (Ramanarayan Vasudevan 15938560) for Question 1
A structure and a union for example cannot be directly translated into assembly language. Even though there is no direct correspondence between these creations in C and  MIPS they are useful because they allow the programmer to   build things quicker than would be possible using MIPS (ie you can build them with MIPS but it is easier to use C).