The correct answer is C. Inter-symbol interference.
Inter-symbol interference (ISI) is a type of distortion that occurs in digital communications when the signal from one symbol overlaps with the signal from the next symbol. This can happen when the symbols are transmitted too close together, or when there is noise in the channel. ISI can cause errors in the received signal, and can make it difficult to decode the data.
There are a number of ways to reduce ISI, including using a higher bandwidth channel, using a more complex modulation scheme, or using a guard band between symbols.
A. Invisible size interference is not a valid term.
B. Infrared size interference is not a valid term.
D. Inter-shape interference is not a valid term.