LEDs can be used to send and recieve signals, there is a lot of information on the internet about this, and how LEDs can be used as etremely low cost sensors when hooked up to a microcontroller that can pulse across them and measure residual energy.
the bit about the dual trace scope as well, most scopes have only 1 gun that sweeps between the two, but some much more expensive scopes can have 2 guns.
a lot of answers on the test are quite unclear as well...
to be honest, I think that if you failed that test you'd be well within your rights to contest quite a few of those questions if it were for real.