A* search algorithm follows the path with the lowest cost function:
\[
f(n) = g(n) + h(n)
\]
where:
- \( g(n) \) is the cost from the start node to \( n \).
- \( h(n) \) is the heuristic estimate from \( n \) to the goal.
Steps:
1. Start from \( S \), expand node with the lowest \( f(n) \).
2. Expand \( A \) (cost 4) and \( E \) (cost 1).
3. Since \( E \) has the lower \( f(n) \), expand \( E \) first.
4. Continue expanding the node with the best \( f(n) \) until reaching \( G \).
Following these rules, the correct expansion order is S, A, E, B, C, D, G.
Conclusion:
The correct answer is (3) S, A, E, B, C, D, G based on A* search expansion.