The observed frequency increases when the source and observer approach each other and decreases when they move apart. this is called the what?
1) emission spectrum
2) doppler effect
3) wavelength

In exchange for land, a knight agrees to be a sort of sub-vassal to a vassal. this agreement was known as: investiture homage tyranny subinfeudation

Examine extracts from the bible which demonstrate the principal beliefs of christianity

In e. c. tolman's experiment, some rats were trained to run through mazes for standard food goals, while other rats were allowed to explore the mazes for 10 days without food goals or other rewards. later, when food rewards were placed in a box at the far end of the maze, the previously unrewarded rats reached the food box as quickly as the rewarded rats after only one or two trials. this experiment demonstrated that the rats had the ability to form of their surroundings.