D is the right answer I took the test. GOOD LUCK
Answer:
the heart pumps more blood and sends it to the muscles. to create more blood more oxygen is used and you start to breathe harder. if you work out hard then you might get some lactic acid build-up.
hope this helped!
To find the mean you add all of the numbers together and then divide that number by how many numbers there are. in this case it would be 441/6= 73.5
2.) 0.2 cm to 6.4 cm
3.) Pebbles
4.) 10 cm/s