Above the Clouds, 'A' is correct. Temperature correction for True Altitude only applies to the *air* column, and not any Terra Firma between the bottom of the column and sea level.
Charliegolf, you can fly across the US without submitting any form of flightplan and not talk to anyone provided you avoid D, C, B & A airspace. If within 30nm of certain designated airports then you must have a transmitting Mode C transponder (but still needn't talk to the controller if you stay outside the controlled airspace.
Most of the country is Class G or E. To a VFR pilot Class E is transparent unless you avail yourself of radar advisory services. If, while VFR in Class E, you choose to communicate with a controller then you must obey the controller's instructions, no different to other airspace.