As the pressure of an enclosed gas decreases to half its original value

To wordsa sentence is made up of a variety of words.

Frequency is the number of complete oscillations of a wave per second.

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.