What’s an example of an experimental scientific investigation

This is my mixture= a type of liquid you mix up for example salt and water is a mixture cause your mixing it up

Which of the following is an example of an opposing signal? no examplthates given.   i would say, that traffic lights in a city at major intersections direct the flow of traffic in opposite directions so would be an example.also, stop signs on either side of the same street would be an example. at a train crossing, the light for allowing car traffic in opposite directions or not would be another example.

The answer should be d if i’m wrong i’ll change my answer and fix it for you