What can occur when two copies of a signal wave arrive at the receiver at the same time, but 180 degrees out of phase which each other?

What can occur when two copies of a signal wave arrive at the receiver at the same time, but 180 degrees out of phase which each other?
A . Increased signal amplitude
B . Bits may be added to the total count
C . Increased signal strength
D . Signal nulling or cancellation

Answer: D