Answer:
A. Red and blue
Explanation:
Theodor Wilhelm Engelmann, born in 1843 and died in 1909, was a German scientist. He was the scientist who detected which wavelengths of light produced the best photosynthetic activity in green alga. In his experiment, Engelmann exposed the photosynthetic algae to different wavelengths in the light spectrum. He then added aerobic (oxygen-dependent) algae to see where they will accumulate the most in order to detect the best wavelength for algae photosynthesis.
He discovered that the aerobic bacteria accumulated in the parts of the algae exposed to red and blue wavelength of light. This is because the algae exposed to the red and blue light produced more oxygen due to increased photosynthetic rate. This attracted the aerobic bacteria, which needs oxygen, to that particular area with that wavelength.
