Sample answer：

　　The book that I think is the most useful is OG, Official Guide for new TOEFL. I'm a book lover and have lots and lots of collections. But OG is of the greatest use ‘cause I'm taking TOEFL Test, which is a must for a student who is gonna finish his or her overseas study in America. Not only does it give the brief introduction of the test, but it also provides test candidates with practical tips. On the other hand, some basics of English language are offered following the main parts, which is very helpful for those who don't have a good command of English. Most of all, it helps me get well prepared for TOEFL iBT and improve my performance on the four skills as well. This definitely leads to the academic success in my future study. That's why I think OG is the most useful book for me.