In Figure E6-1, which is the schematic symbol for an N-channel dual-gate MOSFET?

Explanation

Symbols 4 and 5 are both dual-gate devices, each drawn with two separate insulated gate bars labeled G1 and G2 alongside the channel, so the choice between them turns entirely on the substrate arrow. It points inward, toward the channel, on symbol 4, which is the N-channel marking, and outward on symbol 5, which makes that one P-channel; symbols 2 and 6 carry a single gate and cannot be dual-gate MOSFETs at all.