Hydrologists know that the flow rate of a river is affected by the downhill slope and the width of the river’s channel. Consider an experiment in which scientists use model channels to test the following hypothesis: Water will flow more quickly through a narrower channel. What is the independent variable in this experiment, and what two variables should be controlled? Select the correct response.

answer:   option a) glucagon was secreted by his pancreas before he ate the cookies because blood glucose was low. insulin was secreted after he ate the cookies because his blood glucose was high.

explanation:

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.