Which statement best describes the events of september 11th?

a. the attacks were unexpected by the american public.
b. the attacks destroyed several government buildings.
c. the attacks happened in spite of strong airline security.
d. the attacks worsened us relations with al-qaeda.

Ascientist performs an experiment where she measures the mass of a piece of metal, pours acid onto the metal, washes the metal, and then re-measures the mass of the metal. the scientist repeats the experiment several times, each time increasing the amount of acid used. the dependent variable in the experiment is the: initial mass of the metal final mass of the metal amount of acid used washing the metal