What does the optimization has to do with the PORTABILITY of code. Why would you want to optimize the code just to make that portable !!
Your GENERATING the intermediate code itself ENHANCES the portability of the front end and hence the code. Optimization is something that does not matter in case you are talking of portability.
So even if you DON'T optimize your intermediate code further that is nowhere going to harm your portability. According to me optimizations on intermediate codes are easy and a wide range of optimizations are actually available for INTERMEDIATE code only because it is EASIER to optimize intermediate code rather than machine code where you need to consider the machine architecture as well.
So answer to this question is (B).