Number 3 but technically scientists use rocks to see the age of fossils. hoped this helped!!!:-)
Answer: It's an EXPERIMENT
Explanation: Experiment is done when we apply anything to a samples or conditions in other to study another sample or conditions.
Observation is done when, we study samples or conditions in it's natural way, without application of anything that may alter it's result.
Because the researcher has applied fertilizer to one side and did not apply to the other side, that means he has performed an experiment. Since he wasn't observing the two sample in it's natural way without any external application.
Low pressure weather systems. Warm, wet air begins to rise into the air, and the more it rises, the cooler it becomes, and water vapor in the air forms drops- this is called condensation. The drops join together to form rain, hail, sleet or snow.
For a thunderstorm to form, the air has to be full of moisture, and there has to be an approaching cold front. Finally, the warm air that rises has to be warm enough to stay warmer than the air is passes through. When these three conditions are met, clouds form and a storm begins.
