Here are some things you missed on the quiz and we think you should review.
You should recognize that enzymes typically end with –ase and so you can see that the figure provided indicates the 3 enzymes that are catalysts for the three reactions as shown.
Understanding Ornithine >
On the Surface: In the previous question, we established that the enzyme argininosuccinase must be functional for both strains and that means that argH is not defective (no mutation) for either P or Q. Thus any answer choice suggesting an argH mutation is incorrect.