Validity of an experiment is based upon: a. performing a fair test, in which only the dependent variable affects the independent variable. b. using multiple independent variables. c. using a control group. d. performing a fair test in which only the independent variable affects the dependent variable.

answer: electrons

the answer is neither ball has a charge.

because if they were both positively charged, they will repel each other.

if they were positively and negatively charged, they will seek.

there is no correct list among the choices you've provided.

the list might look something like this:

-- baby human

-- piccolo

-- flute

-- soprano singer

-- trumpet

-- tenor singer

-- trombone

-- baritone singer

-- baritone horn

-- bass singer

-- tuba

since i had to make up the list myself, i made it easy on myself, and i didn't try to shuffle the string instruments and woodwinds into it too.

area of focus