Which one out of the 4 answers

One common educational practice is to chart students' progress over time so that students can see their own improvement. these progress charts often lead to higher student achievement in the absence of other observable forms of reinforcement. the effectiveness of such charts in changing behavior illustrates the role of reinforcement as:

Define production possibility curve

1of the following choices, which one best describes one way that christianity came to east africa? a. christians traveled in caravans through the sahara desert and introduced the people of mali to a new religion. b. christian traders from the mediterranean interacted with the people of axum. c. christian military from west africa traveled across the continent to bring their religion to the people of east africa. d. christian rulers from asia traveled to east africa to bring their religion to the people. 2 which trade item from outside the region did west africans need most? a. gold b. camels c. salt d. iron