In ______ schemes, the voltages are on the both sides of the time axis. For example, the voltage level for 0 can be positive and the voltage level for 1 can be negative.

In ______ schemes, the voltages are on the both sides of the time axis

1.	In ______ schemes, the voltages are on the both sides of the time axis. For example, the voltage level for 0 can be positive and the voltage level for 1 can be negative.
A.	polar
B.	bipolar
C.	unipolar
D.	all of the above
Answer» B. bipolar