To restore nitrogen to the soil, fields should occasionally be planted with what

Legumes

Explanation:

Legumes, leguminous plant that belong to Fabaceae botanical Family (e.g. beans, peanuts, turnips, cloves) , are excellent for restoring the fertility of the soil as they can increase nitrogen soluble compounds within the soil.

They manage to do so because they can establish symbiotic relationships with nitrogen fixing bacteria present in its root nodules. These particular bacteria (e.g. cyanobacteria) can take atmospheric (gaseous) molecular nitrogen and fixed it. This means that these bacteria can transform gaseous nitrogen into a soluble compound that can be retained by water within soil and thus can be absorbed by plant roots.

Nikita Khrushchev.

Explanation:

When an American U-2 spy plane flown by pilot Francis Gary Powers was shot down by the Soviet forces, the American government denied it's involvement in any political warfare, insisting that it was just a weather research aircraft.

But when the aircraft was checked, it was found that it had done a recon on Soviet places, taking pictures before it was shot down. This led to the president Dwight Eisenhower to try to employ a brinkmanship policy against the then Premier of the Soviet Union, Nikita Khrushchev. A brinkmanship is a form of international political issue that involves one leader/ side trying to outdo the other/ enemy in the arms race. This led to a much more serious issue of trying to be stronger in regards to arms between the two powers.