Sharp Writing: Build Better Writing Skills/ Kaplan Publishing (you can find it at Iowa Book)
This is a really good reference book for those who need to brush up or re-learn writing skills for all formats/types of writing.
The first step of the book is their Building Block Quiz which determines what you know. Step 2 involves lessons where you review your old skills and learn new ones. Building Block 3 puts the new skills to the test. The end of each chapter has a test to assess your knowledge.
The book is divided into sections like Structure, Syntax, Diction, Clarity, Tone, Usage, etc. It also goes through the writing stages: prewriting, writing, revising,editing and proofreading.
Most importantly it discusses resumes, cover letters, proposals, memos, and business letters.
Many PR internships and jobs require a writing test and this book provides great practice so if you need to brush up on your skills, check it out.