I believe that the best answer to this question is d. amino acids.
Answer:
It's important for a scientist to try to hold all variables constant except for the independent variable. If a control variable changes during an experiment, it may invalidate the correlation between the dependent and independent variable. When possible, control variables should be identified, measured, and recorded.
Answer:
C) period
Explanation:
Groups are columns on the periodic table (with the same number of electrons on the outer shell of the elements), whereas periods are rows (increasing in atomic number by 1 - 5, 6, 7, 8, 9 etc.)
