Based on the principles of experimental design addressed in Appendix4,
Step 1,select the correct description for Design C below.
Design C
1.Variable Treatment 1Treatment 2
2.concentration of heavy metals in soil (ppm) 0 ppm 300ppm
3.concentration of nitrogen in soil (ppm) 40 ppm 40 ppm
4.concentration of water in soil (%) 36% 36%
5.temperature of air (\deg C) 15\deg C 30\deg C
6.light intensity (lux) 3000lux 3000 lux

a.Best design, only one variable is different
b.Best design, two variables are different
c.Not a good design, no variables are different
d.Not a good design, two variables are different