Plants grow in a soil with a typical pH value between 5.5-8. Levels below or above that do not allow plants to thrive. What can cause a decrease in the pH level of soil?
A)
no-till farming
B)
accumulation of heavy metals
the growth of fungi and bacteria
D)
Applying phosphorus fertilizer in small amounted

The independent variable is the type of music.the dependent variable is the pulse rate.the intervening variable is the age of the subject.if the mother does not like rock, her pulse is likely to not increase.the same might be true for the sister.the friend may like rap and gets excited.to establish cause/effect relationship, all of the subjects must be consistent.hope i .