Radio waves- radios
Microwaves- microwave ovens
Visible light- flash light, rainbows
X-rays- instrument used for science
D, as he is testing which type of fertiliser is the best, and hence it should be the only changed variable. Everything else should remain the same.
The basic metric unit for mass in the kilogram
Answer:
1) ironing a shirt 2) writing on surfaces 3) working of an eraser