What forms the eastern tectonic boundary of the North American plate?

to the east the north American shares the mid atlantic ridge with the Eurasian plate

the answer is b. apsidal precession

radiative zone

explanation    

radiative zone is the layer of the sun which energy is transferred away from the core by radiation. although, the core is the only part of the sun that produces an appreciable amount of heat through fusion. in fact, 99% of the energy produced by the sun takes place within 24% of the sun's radius.