How do scholars know that vikings had traveled to north america prior to columbus’s voyage

How many people in the world’s economy work in “system d”?

Which of the following statements describes the nature of "stigma" as it relates to welfare? a) society values individual characteristics such as self-reliance and a willingness to work hard, welfare recipients are seen as dependent and lazy. b) social welfare hs been polarized as a "moral category", and its related policy includes treating the poor in a dignified manner, as to highlight the responsible nature of the welfare recipents. c) the norm of reciprocity explains the societal obligation to make some return for the things received, welfare recipents are stigmatized because they are able to be seen as making appropiate contributions for the benefits they incur. d) the capitalistic nature of u.s. society stresses that those who work hard and have the ability will be rewarded with success, welfare recipients are equal to those who do not receive welfare because both groups of people deserve the benefits of success.

As our current atmosphere formed, the concentrations of various atmospheric gases fluctuated. match each gas with the explanation that best describes how its proportion changed during the evolution of the atmosphere.