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To understand this question, one must understand that cancer is a directly result of over proliferation, which essentially means actively going through the cell cycle more than expected. Thus, the cells that are least likely to become cancerous are those that themselves don’t divide as frequently; after all, how can you get over proliferation of a cell that itself does not tend to divide more than once? So now, the question is essentially reduced to which of the cells mentioned are the ones that tend to divide the least? The answer is A because neuronal cells do not divide after differentiation; in fact, they tend to enter a G0 stage where they stay for the remainder of their life. On the other hand, intestinal epithelial cells (or just any epithelial cells in general) are consistently regenerating because they are needed for proper digestion/protection (which makes them a potential cancer source); similarly, alpha and beta pancreatic cells are also potentially cancerous because they are needed for the proper glucose regulation. 

For this reason, a neuronal cell is least likely to become and A is the correct answer.