#and-or-graph

Question 1: Single choice

AO* searches an AND/OR graph. The root has heuristic value 39 and two ways to be solved: an OR edge to node X (heuristic 23), or an AND arc (hyperedge) that requires both node Y (heuristic 4) and node Z (heuristic 8). Every edge costs 10. Which node(s) can AO* expand (refine) next?

Y and Z, the leaves of the AND arc1
X only, the leaf of the OR edge2
X, Y and Z, since all three are unexpanded leaves3
The root again, because its value 39 overestimates both options4

Timed test