You are building a shelf at home. as you sand the wood dust floats into the air. the air and dust from sanding create which of the following.
a. a solution
b. a pure substance
c. a colloid
d. a suspension

A colloid and a suspension are the same thing so it rules out c and d because the dust is heavier than air causing it to float down but not float constantly. a pure substance is one solid substance. so its be A. a solution. a solution is a homogenous mixture of 2 or more substances because it wouldn't only compose of wood dust because of the air oxygen and carbon dioxide keeping it from falling faster.

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 .