A few readers have asked me whether there’s an answer key to Grammar Choices for Graduate and Professional Writers. There is: we published it as a Commentary online only (saves trees and cost!). You can find it on the University of Michigan Press’ teacher materials page. I provided answers to all the closed item questions and sample sentences for some of the more open exercises, as well as explanations, cross references, and teaching notes.
Do let me know if you spot any mistakes, or if you have any questions about the exercises!