You can change answers with in a block in allotted block time but the only EXCEPTION is for sequential set of qs where once you go for option, you cannot change answers for that question..
you MAY encounter Sequential Qs in step 1 or ck and clinical vignette may be associated with two or three consecutive questions. Each question is associated with the initial patient vignette but is testing a different point. You are required to select the ONE BEST answer to each question. Questions are designed to be answered in sequential order. You must click “Proceed to Next Item” to view the next item in the set; once you click on this button,the next question will be displayed, and you will not be able to return to the previous question or change the answer to it.
You can change answers for Single item qs in a given block
You cannot change answers for Sequential item sets in a given block
Thank you