If you want to be in the market, it is recommended to buy Optimal Design. Its content is from shallow to deep, and the topic is moderate, which is very suitable for your own practice and consolidation. The matching loose-leaf book is also very convenient to use!

If you buy it online, it is recommended to buy "Famous Teachers Accompany You", which explains it comprehensively and analyzes the answers in detail. It's best to make a unit paper, such as Gui Zhuang Red Book, which is a very practical book!