The Period $T$ Of the Fundamental Mode of the Air in a Pipe

Multiple Choice

The period $T$ of the fundamental mode of the air in a pipe open at one end and closed at the other is equal to what multiple or fraction of the time $\Delta t$ required for a sound wave to travel from one end of the tube to the other?

A) $T=\Delta t / 4$
B) $T=\Delta t / 2$
C) $T=\Delta t$
D) $T=2 \Delta t$
E) $T=4 \Delta t$