Given a scientific question, generate a correct answer to it.

[Q]: What kind of interference is observed when the paths differ by a whole wavelength, and the waves arrive in phase?
[A]: constructive interference

[Q]: The pion can only be created by violating the conservation of what?
[A]: mass-energy

[Q]: Plants can tell the time of day and time of year by sensing and using various wavelengths of what
[A]:
sunlight