A source, approaching with speed \( u \) towards the open end of a stationary pipe of length \( L \), is emitting a sound of frequency \( f_{s} \). The farther end of the pipe is closed. The speed of sound in air is \( v \) and \( f_{0} \) is the fundamental frequency of the pipe. For which of the following combination(s) of \( u \) and \( f_{s} \), will the sound reaching the pipe lead to a resonance?
