According to one acid-base theory, water acts as an acid when an h2o molecule
(1) accepts an h+ (3) accepts an h-
(2) donates an h+ (4) donates an h-

The answer is (2) donates an H+. First, the hydrogen ion is usually positive. Then, the theory means that acid donates an H+ and base donates OH-. So because water molecule can donates an H+, it is an acid.

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 .