2.1 x 10^-3 x 2 x 10^2 = a)
4.2 x 10^-5

b)
4.2 x 10^-1

c)
4.2 x 10^1

d)
4.2 x 10^-6

I believe it is B

Explanation:

hope it helps. please let me know if it's wrong

one state would change   like louisiana to texas. thats a change

explanation:

the old alchemists made significant contributions to science even though there starting premises were off a bit. their conclusions after failure would steer them into better directions for investigation. science is no more than close observation and the initial mistakes result in rethinking and retrying experiments.