Re: How to do the homework?
@Hillbilly, I don't want to overstep on this topic. But have a look at problem 9 (in the second homework set). Start from the target function:
f(x1, x2) = sign(x1^2 + x2^2  0.6)
Notice that it's symmetric in x1 and x2? What's that suggest to you about choices b, c, and d? Why would the two strongest coefficients in the polynomial differ by tenfold between these variables? And choice e, how does the x1x2 term become so significant compared to the others? In fact, what would the geometric significance of the x1x2 term be in terms of classification?
Let's also look at problem 10, which uses the same target function and illustrates a similar point. The target function wasn't originally linearly separable, but your transformation definitely made it so. This means you're running linear regression on a linearly separable set of data, and you have a fairly large set of it. How much error will this result in? A lot? Medium? Very little? But the target function has 10% noise, which depending on what you decided on my last question, E[out] will be 10% + a lot, 10% + somewhat, or 10% + negligible.
In general, it is not easy to write multiplechoice problem sets on advanced topics. Just ask the folks who write questions for the SAT! Not long ago, it was possible to answer reading comprehension questions without reading the passage  just pick the answer which wouldn't cast any group of people in a bad light. It was also possible to identify (and skip) entire sections of the exam which would not be graded.
