2. To make observations, an observer must always use

(1)experiments
(2)the senses
(3)proportion
(4)mathematical calculations
Is it (2)?

Right!

Their sense

Thanks!

mathemathical caculations

experiments

Yes, you are correct! To make observations, an observer must always use their senses. Observations involve using our senses such as sight, hearing, touch, taste, and smell to gather information about the world around us. By using our senses, we are able to perceive and notice things that occur in our surroundings, which is essential for making accurate observations.