What instrument can detect an upcoming tornado

A Doppler radar is an instrument that can detect an upcoming tornado. This technology uses a velocity to measure a certain speed of an object that's why it can detect if a tornado is coming if the velocity of an air is getting faster that its normal speed.

the correct answer is modern american cars are not available due to trade restrictions.

trade between cuba and the united states have serious restrictions. the u.s. imposed an economic embargo on cuba, that among other things means that modern american cars are not available due to trade restrictions.

in response to some governmental actions of the authorities from cuba, president john f. kennedy proclaimed an embargo on trade between both countries in february 1962. the trade embargo remains active until this day and was implemented directly by the departments of commerce and the department of treasury.

in president trump’s administration, there is a national security presidential memorandum that "strengthens the policy of the u. s.", affecting trade with cuba.

i would say b. research typically uses a variety of sources