Which of the following is an example of frontier research?

What challenges did you encounter during the circuit training program?

The image shows a pendulum in simple harmonic motion the pendulum starts at a and swing to e

Starting with only the balmer series light (visible light), how could we ensure that the solar panels generate a current that mark can use for his power station? a)by gradually increasing the brightness (amount) of light that we shine on it. b)by gradually increasing the frequency of the light we shine on it. c)by gradually increasing the wavelength of the light that we shine on it.