@ramkiarchu
The reason I strongly recommend the Keith Williams books is so that you develop a solid foundation in solving problems . He also clearly explains how the answers are solved or obtained something which is not available in other books
@Pilotbaba
The oxford books and Keith williams books does not cover the entire JAA question bank . If you want more JAA questions have a look at the following
Aviation Jobs | AviationTire.com
This website although not free is worth the investment as it lets you practice
This is the official JAA CQB v15
EASAbank.eu, the free QCB v.15 for european airplane pilots