The U$.$S$.$ Border Patrol ground sensor program includes a broad range of remotely monitored sensors placed in areas along the border where Border Patrol Agents are not always present. Typically, the sensors are concealed above or immediately below the ground. Some of the sensors include capabilities to detect activity close to the ground or in areas immediately off shore.

From the information given above, it can be validly concluded that

A$)$ ground sensors are always concealed above or immediately below the ground

B$)$ devices with the ability to detect activity close to the ground or in areas immediately off shore are never considered to be ground sensors

at least some devices concealed above or immediately below the ground are ground sensors

D$)$ some devices with the ability to detect activity close to the ground or in areas immediately off shore are not ground sensors

E$)$ at least some devices concealed above or immediately below the ground are not ground sensors