How to wait for thread?

I'd like the main thread to wait until these three threads have
completed their task:

LoadOjbects lo = new LoadOjbects();

lo.thrd1.Start();
lo.thrd2.Start();
lo.thrd3.Start();

while (lo.thrd1.IsAlive || lo.thrd2.IsAlive || lo.thrd3.IsAlive)
{
Thread.Sleep(500);
}

The above works but adds a lot of time to the overall.

Thanks,
Brett

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