How is a unitary system of government different from federalism?
A. In a unitary system, there is one leader who runs the government, but in federalism, leadership is shared among several.
B. In a unitary system, a strong central government controls weak states, but in federalism, the central power is shared with states.
C. In a unitary system, there is no such thing as different forms of leadership, but in federalism, there is such a thing.
D. In a unitary system, a lack of central leadership allows the states to lead in most ways, but in federalism, leadership is limited.

explanation: j

the columbian exchange, also known as the columbian interchange, named for christopher columbus, was the widespread transfer of plants, animals, culture, human populations, technology, and ideas between the americas, west africa, and the old world in the 15th and 16th centuries, related to european colonization and trade following christopher columbus's 1492 voyage. invasive species, including communicable diseases, were a byproduct of the exchange. the changes in agriculture significantly altered and changed global populations. the most significant immediate impact of the columbian exchange was the cultural exchanges and the transfer of people between continents.

the new contact between the global population circulated a wide variety of crops and livestock, which supported increases in population in both hemispheres, although diseases initially caused precipitous declines in the numbers of indigenous peoples of the americas. traders returned to europe with maize, potatoes, and tomatoes, which became very important crops in europe by the 18th century.

the term was first used in 1972 by american historian alfred w. crosby in his environmental history book the columbian exchange. it was rapidly adopted by other historians and journalists and has become widely known.

ecologists usually specialise in a particular area, such as freshwater, marine, terrestrial, fauna or flora and carry out a range of tasks relating to that area. when starting out, ecologists often conduct surveys to identify, record, and monitor species and their habitats.