Pls help me understand this

In 100,000 years, the rotation of earth will be slower by how many seconds?

Mankiw attributes – chapter 1 and his 10 principles – differences in living standards within a countryover time and across countries at a moment in time to: a. the presence or absence of inflation and unemployment. b. the allocation of resources between private markets and the public sector. c. those that have dealt successfully with the efficiency v. equality tradeoff and those that haven’t. d. differences in productivity. e. ones that think at the margin and respond to incentives and those that don’t.

When should you question a sources credibility