The emitter follower or common collector circuit is shown in the figure. C1 and C2 are large enough to be regarded as short circuit to the input AC signal. The output voltage uO and the input voltage ui are (     ).
A、180°out of phase (in opposite phases)，the output voltage is greater than the input voltage.
B、in phase, and the output voltage is less than and approximately equal to the input voltage
C、90°out of phase，The input and output voltages are equal in magnitude
D、in phase, the output voltage is greater than input voltage