I think it would be the fourth answer choice.
Answer:
a pop-up box
Explanation:
A voice command, mouse clicks, or keyboard strokes is the <em>user</em> doing something. But a pop-up box is not. I realize that a popup box could <em>contain</em> a user input, but the box itself is not any sort of user input. It's the opposite.
I think it is.. the low side handwheel is made of blue plastic or occasionally has a blue decal in its center then the high side handwheel is made of red plastic or occasionally has a red decal gauges used with a refrigeration gauge manifold are either analog which resemble other pressure gauges or perhaps digital.... i hope this helps :)
