Also please tell all part must be correct to consider one question correct? Or they will good give mark for partial correct question?
There is no partial credit within a large question. You would need to get all dropdowns/radiobuttons, etc correct for an entire question in order to get credit for that question.
That said, you don't necessarily need to get every single thing correct in order to get a "perfect" 8/8 score.
For practice, please go to: http://www.gmatpill.com/gmat-practice-t ... reasoning/
... and more
What's Inside GMAT Pill?
Zeke Lee, GMAT Pill Study Method (Study Less. Score More.)
GMAT Pill Reviews | GMAT PILL Free Practice Test