How can one prepare for sat subject tests, specifically physics and chemistry?

Did the universe cool off or get hotter as it expanded after the 'big bang"?

The authors use the word “backbone” in lines 3 and 39 to indicate that

The graph shows the populations of two species over time. which type of symbiotic relationship does the graph represent? a. commensal b. mutualistic c. parasitic d. parent-offspring e. predator-prey