When listening to the heart sounds, which of the following activities makes the "lub dub" sound?

"lub" is the AV valves closing, "dub" is the SL valves opening

"lub" is the AV valves opening, "dub" is the SL valves closing

"lub" is the AV valves closing, "dub" is the SL valves closing

"lub" is the AV valves opening, "dub" is the SL valves opening