Which pair of variables shows a clear causal link?
a. ) number of vehicles in a city and efficiency of the working population
b ) room temperature and visual accuracy of a person
c ) movies produced in a year and growth of the pharmaceutical industry
d ) number of defects on a bolt of fabric and number of quality check processes
done

solution:

the given function is ,

      =

the three roots of this quadratic function is , 0 ,8 and 10.all the roots are real and rational.

if a quadratic equation is of the form ,

sum of the roots = a + b +c= 0+8+10=18=  

product of roots taken two at a time = a b + b c+ c a = 0+80+0=80 =  

product of roots = a b c = 0=  

there are 11 doors in a hall starting from 0 to 11.the entry in the hall is permitted through gate number 0 and exit is allowed through only gate number 8 and 10.so, three roots(0,8,10) of quadratic function is given by entry and exit route of this hall.

you didn't give me the choices, so i will just give you the graph so you can look at your choices and choose the right one.