In what altitude structure is a transponder required when operat

In what altitude structure is a transponder required when operating in controlled airspace?

A.Above 12,500 feet MSL, excluding the airspace at and below 2,500 feet AGL.

B.Above 10,000 feet MSL, excluding the airspace at and below 2,500 feet AGL

C.Above 14,500 feet MSL, excluding the airspace at and below 2,500 feet AGL.

正确答案是B