According to the Barkhausen criterion for sustained oscillations in a feedback oscillator with open-loop gain $A$ and feedback factor $eta$, the loop gain magnitude and phase shift must satisfy
(A)
$|A\beta| = 1$ and net phase shift around the loop is $0^\circ$ or an integer multiple of $360^\circ$
(B)
$|A\beta| < 1$ and phase shift is $180^\circ$
(C)
$|A\beta| \gg 1$ and phase shift is $90^\circ$
(D)
$|A\beta| = 0$ and phase shift is arbitrary