A pigeon is presented with a blue key and a red key in alternating order. In the presence of the blue key, it earns food on a VI 200-sec schedule. In the presence of the red key, it earns food on a VI 600-sec schedule. The VI 600-sec schedule is then changed to a VI 100-sec schedule. As a result, rate of response on the VI 200-sec schedule will , which is known as a(n) contrast effect.

The correct answer is "decrease; negative".

Explanation:

If the pigeon changes its eating speed from VI 600-sec schedule to VI 100-sec schedule in the presence of the red key, most likely it will have the same effect in the presence of blue key. The rate of response of the VI 200-sec schedule in the presence of blue key will decrease. This change is known as a negative contrast effect, since the result lowers the eating speed of the pigeon.

i'm thinking (a) to keep sand in place; ////////////

explanation: a sand fence or sandbreak, like a snow fence, is used to force windblown, drifting sand to accumulate in a desired place. sand fences are employed to control erosion, sand dune stabilization, keep sand off roadways, and to recruit new material in desert areas.

there’s no image attached but i can if you want: )