Mark sees an attacker approaching him with a knife. during his reaction, he experi-ences increased energy and a faster heart rate. this is caused most directly by

Sally and sue were investigating the topic of friction in science. they used a small car and a ramp as seen in the picture to test what they were learning. they knew that they slipped easily on waxed floors but not on carpet, so they decided to change the material on the surface of the ramp to see what happened. they planned to use glass, carpet, aluminum foil, and sandpaper and run the car down the ramp over each surface. what would be the best research question to guide the girls' experiment? a) does the amount of surface area affect the friction on the moving car? b) will the car travel fastest on the glass surface? c) how does the angle of the ramp affect the speed of the car? d)do rougher surfaces tend to create more friction than smooth surfaces?

Explain how the number of similarities between the embryos from early stage to late stage is used as evidence of a common ancestry

In which of the following relationships is one organism always benefited while the other organism is always harmed