What characteristics should a good evaluation function h for A* have? Explain reasoning.

Assume A* is used with a heuristic h(s) that sometimes overestimates the cost of reaching the goal state from s. Will A* in this case still find the optimal solution? If your answer is yes, give your reasoning. If your answer is no, give an ex of a search problem with the above characteristics for which A* no longer finds the optimal solution

Assume h1 and h2 are both admissible heuristics for A* for a search problem; is h(x)=max(h1(x), h2(x)) also an admissible heuristic? Do you prefer heuristic h over heuristics h1 and h2 or not? Explain your reasoning