What did muslim leaders and scholars do to preserve and expand knowledge and learning?

They kept all their wisdom written down and there is still their language here today to decode what they said.

Explanation:

While in Christian Europe the Greek and Roman sources of wisdom were ignored (actively or passively), Muslim leaders brought them together in Baghdad and Cordoba and translated them into Arabic. Once again, when European states were mentally prepared for this material, they could easily acquire it from the Muslims, who had kept it on in the interim.

even though you have attached neither the chart nor the generalizations, i have located them online. the right answer is d, since they are asking you about a generalization. you can only infer from the chart that between 2008 and 2009 the number of employed workers decreased significantly (from over 115 millions to 107 millions approximately), which signals some type of economic crisis.