Ascientist performs a controlled experiment. this means that select one: a. the experiment is repeated many times to ensure that the results are accurate. b. the experiment proceeds at a slow pace to guarantee that the scientist can carefully observe all reactions and process all experimental data. c. two versions of the experiment are conducted, one differing from the other by only a single variable. d. one experiment is performed, but the scientist controls the variables.

d. One experiment is performed, but the scientist control the variable.

Explanation:

In the controlled experiment the independent variable is changed in an orderly manner so that accurate changes can be observed on the dependent variable. Also in this a controlled group is also used for comparision with the changes in other variables.

the atmospheric gas that forms a mild acid when dissolved in water is called carbon dioxide. the correct answer is a. 2.) chemical weathering would cause an inscription on a marble headstone to become harder and harder to read over time.