8. Humans need oxygen to break down food in order to provide energy for cells. The oxygen needed for this process is delivered by an organ system called the A. respiratory system. B. lungs. C. digestive system. D. alveolus.

B

Explanation: we use lungs to breathe, so we take oxygen by lungs.  

i had this question and the answer was 3.15 miles.

martina travels from school to her mom's office. from there, she walks to school. after school, she walks to the library and then to a friends house before finally ending back at home. find martina's total distance traveled.

a) 0 miles  

b) 0.4 miles  

c) 1 mile  

d) 3.15 miles

one person pulls 90n one way and the other has 100n pulling the other way.

so the net force = 90 - 100 = -10n,

or the ans can be 10n if the picture shows -90n and 100n instead.