Which among the following statement(s) is(are) FALSE?

A. Greedy best-first search is not optimal but is often efficient.

B. $A^*$ is complete and optimal provided $h(n)$ is admissible or consistent.

C. Recursive best-first search is efficient in terms of time complexity but poor in terms of space complexity.

D. $h(n)=0$ is an admissible heuristic for the $8$-puzzle.

Statement A is true because greedy best-first search is generally not optimal, but it is often efficient.

Statement B is true because $A^*$ is optimal when the heuristic is admissible, and consistency is a stronger condition.

Statement C is false because recursive best-first search uses less memory, so it is good in terms of space complexity, but it may be poor in time because nodes can be regenerated.

Statement D is true because $h(n)=0$ never overestimates the actual cost, so it is admissible.

Therefore, only statement C is false.